This PDF file contains the front matter associated with SPIE Proceedings Volume 7945, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing

We have discovered that helium-4 crystals are anomalously soft around one tenth of a Kelvin (100 mK) if totally free of impurities. Their plasticity is large, due to quantum effects. This is because their dislocations can move macroscopic distances (typically 0.1 mm) at high speed (meters per second) under the effect of stresses as small as 1 microbar. In classical crystals all atoms are completely frozen at low temperature. But in quantum crystals such as helium-4, quantum fluctuations are large and atoms can jump by quantum tunneling from site to site, especially at the core of dislocation lines where the packing is not as compact as elsewhere. We have shown that highly mobile dislocations reduce the stiffness of helium-4 crystals by one order of magnitude. However, very tiny traces of helium-3 impurities are sufficient to stop the motion of dislocations when they attach to them below temperatures of order 100 mK. Apparently, this is what drives these crystals to a "supersolid state", an astonishing new state of matter where superfluidity coexists with crystalline order. We think that the core of dislocations becomes superfluid only when the dislocation lines themselves stop moving.

This presentation introduces a chemical analyzer (The ERACHECK) which is based on quantum cascade laser technology for measuring oil-in-water. Using these mid-IR lasers, it was possible to develop a portable, robust and highly precise analyzer for the measurement of oil-in-water, a parameter which is vital in the petrochemical industry for process control and environmental analysis. The overall method employs a liquid-liquid extraction step of the aqueous sample using a cyclic, aliphatic hydrocarbon such as cyclohexane. Quantification is based on measurement of the C-H deformation vibrations of the extracted hydrocarbons in the cyclic extraction solvent. The developed method is linear from 0.5 - 2000 ppm of oil in water, with precisions well below 15% in terms of r.s.d for repeated measurements. The portability of the ERACHECK and its robustness has been key for its successful use on oil rigs as well as petrochemical production sites on land. The values provided by the ERACHECK correlate well with those obtained by the former CFC (Freon 113) based method for oil in water, which is no longer in use in industrialized countries due to the ozone depleting effect of the CFCs employed.

Recently, we have demonstrated that the "intrinsic" linewidth of Quantum Cascade Lasers (QCLs) can go beyond the radiative lifetime of the upper level. This represents the first demonstration of a sub-radiative linewidth for any laser. The intrinsic linewidth of a QCL can be as narrow as hundreds Hz, paving new ways for ultra-sensitive and precise harnessing and detection of molecules. We are working towards full exploitation of such intrinsic properties by designing appropriate phase-lock loops and enhancement-cavities for interaction with molecules. Combination with optical-frequency-comb-synthesizers and appropriate spectroscopic techniques, like saturated-cavity-ring-down-SCAR or polarization spectroscopy can provide unprecedented sensitivity and frequency accuracy for molecular detection.

We show that QC laser could improve capillary Gas Chromatography Infrared spectroscopy resolution significantly, i.e. both Doppler limited and Doppler free resolution could be achieved. To achieve these goals, we report our latest efforts in characterizing the tuning and noise properties of Quantum Cascade (QC) lasers; novel schemes on modulation to gain largest tuning range as well as on stabilizing and locking the QC lasers are proposed, and results presented.

Vertical external cavity surface emitting lasers (VECSELs) have captured the interest of high-brightness semiconductor researchers, primarily due to their simplicity in design, power scalability, and "open cavity architecture," wherein it is simple to integrate nonlinear elements into the cavity. Through direct emission and indirect (frequency-converted) means, wavelengths from the UV through to the mid-wave infrared regimes have been demonstrated, increasing the suitability of the VECSEL platform for multiple applications. This presentation outlines recent progress in VECSELs, measurements, novel cavities, and potential applications for these lasers.

We present long-wavelength buried tunnel junction (BTJ) VCSELs for emission wavelengths around 2.3 μm. Two different device concepts have been realized utilizing either InP- or GaSb-based materials. The InP-VCSELs are based on a BTJ-design which has been well-proven for wavelengths up to 2 μm in recent years. To extend this range up to emission wavelengths around 2.3 μm, the main focus is set on an optimization of the active region. In this context, we use a graded and heavily strained quantum well design in conjunction with optimized growth conditions. The photoluminescence and x-ray characterization shows a very good material quality. Room-temperature operated VCSELs exhibit around 0.5 mW of output power with singlemode-emission at 2.36 μm representing the longest wavelength that has been achieved with InP-based interband lasers so far. GaSb-based devices comprise an epitaxial back mirror and a dielectric output mirror while the basic BTJ-principle is maintained. Using GaInAsSb quantum wells, the active region reveals excellent gain characteristics at 2.3 μm. Singlemode VCSELs show room temperature threshold currents around 1 mA and output powers of 0.7 mW, respectively. Both laser types have been implemented in a tuneable diode laser spectroscopy (TDLS) setup to evaluate their capability for sensing of carbon monoxide. Using an absorption path length of only 10 cm, concentration measurements down to a few ppm have been successfully demonstrated.

Low noise-level optical sources are required for numerous applications such as microwave photonics, fiber-optic sensing and time/frequency references distribution. In this paper, we demonstrate how inserting a SC active medium into a centimetric high-Q external cavity is a simple way to obtain a shot-noise-limited laser source over a very wide frequency bandwidth. This approach ensures, with a compact design, a sufficiently long photon lifetime to reach the oscillation-relaxation- free class-A regime. This concept has been illustrated by inserting a 1/2-VCSEL in an external cavity including an etalon filter. A -156dB/Hz relative intensity noise level is obtained over the 100 MHz to 18 GHz bandwidth of interest. This is several orders of magnitude better than the noise, previously observed in VCSELs, belonging to the class-B regime. The optimization, in terms of noise, is shown to be a trade-off between the cavity length and the laser mode filtering. The transition between the class-B and class-A dynamical behaviors is directly observed by continuously controlling the photon lifetime is a sub-millimetric to a centimetric cavity length. It's proven that the transition occurs progressively, without any discontinuity. Based on the same laser architecture, tunable dual-frequency oscillation is demonstrated by reducing the polarized eigenstates overlap in the gain medium. The class-A dynamics of such a laser, free of relaxation oscillations, enables to suppress the electrical phase noise in excess, usually observed in the vicinity of the beat note. An original technique for jitter reduction in mode-locked VECSELs is also investigated. Such lasers are needed for photonic analog to digital converters.

Integrated terahertz (THz) pulse generation and amplification in a THz quantum cascade laser (QCL) is demonstrated. Intra-cavity THz pulses are generated by exciting the facet of the quantum cascade laser with an ultrafast Ti:Sapphire laser (~100fs) and detected using electro-optic sampling. Maximum THz field emission is found with an interband transition of 1.535eV (809nm) and by narrowing the excitation laser bandwidth to ~3THz. These resonance conditions correspond to the narrowband excitation of the quantum cascade miniband, indicating that the THz pulse is generated by the photo-excited carriers that are accelerated by the applied field. The generated pulse is subsequently amplified by the narrowband gain of the laser as it propagates through the QCL cavity. As an integrated THz generator-amplifier, the technique avoids the issues associated with the coupling of external THz pulses into sub-wavelength dimensioned cavities.

For many practical applications that need bright sources of mid-infrared radiation, single mode operation and good beam quality are also required. Quantum cascade lasers are prominent candidates as compact sources of mid-infrared radiation capable of delivering very high power both CW and under pulsed operation. While 1D photonic crystal distributed feedback structures can be used to get single mode operation from quantum cascade lasers with narrow ridge widths, novel 2D photonic crystal cavity designs can be used to improve spectral and spatial purity of broad area quantum cascade lasers. In this paper, we demonstrate high power, spatially and spectrally pure operation at room temperature from narrow ridge and broad area quantum cascade lasers with buried 1D and 2D photonic crystal structures. Single mode continuous wave emission at λ = 4.8 μm up to 700 mW in epi-up configuration at room temperature was observed from a 11 μm wide 5 mm long distributed feedback quantum cascade laser with buried 1D gratings. High peak powers up to 34 W was obtained from a 3mm long 400 μm wide 2D photonic crystal distributed feedback laser at room temperature under pulsed operation. The far field profile had a single peak normal to the laser facet and the M² figure of merit was as low as 2.5. Emission spectrum had a dominating single mode at λ = 4.36 μm.

Demand on high quality and new contents in optical internet still requires continuous development of advanced optical components in the point of low cost and high performance. The use of quantum dot structure in the active region of semiconductor optical devices have been shown superior high carrier dynamic and temperature less sensitive properties by some research groups. A 1.5μm QD laser on the InP(100) substrate will be demonstrated in detail with the brief review of new achievements of QD optical devices in the near IR wavelength range. Enhanced temperature stability of Fabry-Perot QD laser will be reported. Also, 10Gbps direct modulation speed demonstrated with the moderate side mode suppression in the DFB QD laser. Statistic approach for the reproducible formation of quantum dot in the MOCVD and MBE system also will be introduced

There are two particularly promising approaches to reach laser emission in the 3.0 - 3.5 μm wavelength range with application grade performance; GaSb based laser structures using GaInAsSb / AlGaInAsSb type-I quantum well (QW) active region, as well as type-II interband cascade (IC) material have been investigated and corresponding results are discussed in this paper. We also present different techniques for the fabrication of spectrally monomode distributed feedback (DFB) lasers for sensing applications in the targeted wavelength range. Based on the different waveguide designs of the two material approaches, different concepts to achieve monomode emission were applied: lateral metal gratings were used for type-I laser structures, vertical sidewall gratings for ICL designs. The fabrication procedure, including growth of the laser structures by molecular beam epitaxy, device processing and characterization, are described in the following. DFB emission under continuous wave (cw) operation was achieved up to room temperature (RT) in the target wavelength range. Sidemode suppression ratios (SMSRs) exceed 30dB for the fabricated devices and mode-hop free monomode tuning ranges of several nanometers are demonstrated.

Planar 2D photonic crystals are of tremendous interest for integrated optics applications. In the last years, several possible laser cavities have been proposed in that prospect. In this paper, we review our work on 2D photonic crystal second order DFB lasers. We will show that an affine deformation of the photonic crystal allows the fabrication of closely spaced arrays of high Q DFB lasers. Combining waveguide and photonic crystal affine deformations, we demonstrate arrays of optically pumped single mode DFB lasers with controlled wavelength spacing. Potential extension of this scheme will be discussed, altogether with potential for electrical pumping implementation.

We report on novel methods employing a modulation cancellation technique which result in a significantly increase in the sensitivity and accuracy of trace gas detectors. This method can be applied for isotopomer abundance quantification, temperature measurements and the detection of large molecules.

The monitoring of acetylene (C₂H₂) concentrations is important for many chemical processes. Industrial trace gas measurements are usually performed using gas chromatographs (GC) which have time constants of several minutes. Optical analyzers are expected to yield faster response times with lower maintenance costs. We investigated the use of quantum cascade laser (QCL) spectroscopy in the 14μm range for the sensitive and fast detection of C₂H₂. This spectral range is favorable, as it avoids spectral interferences by other components which could be present in typical process gases. We developed new custom DFB QCLs and characterized their spectral properties. We determined the performance of our QCL gas analyzer setup and demonstrate a noise equivalent concentration of 10 ppb in 20 s average time.

A continuous wave, thermoelectrically cooled, distributed feedback quantum cascade laser (DFB-QCL) based sensor platform for the quantitative detection of ammonia (NH3) concentrations present in exhaled human breath is reported. The NH3 concentration measurements are performed with a 2f wavelength modulation quartz enhanced photoacoustic spectroscopy (QEPAS) technique, which is very well suited for real time breath analysis, due to the fast gas exchange inside a compact QEPAS gas cell. An air-cooled DFB-QCL was designed to target the interference-free NH3 absorption line located at 967.35 cm^-1 (λ~10.34 μm). The laser is operated at 17.5 °C, emitting ~ 24 mW of optical power at the selected wavelength. A 1σ minimum detectable concentration of ammonia for the line-locked NH₃ sensor is ~ 6 ppb with 1 sec time resolution. The NH₃ sensor, packaged in a 12"x14"x10" housing, is currently installed at a medical breath research center in Bethlehem, PA and tested as an instrument for non-invasive verification of liver and kidney disorders based on human breath samples.

We report the molecular beam epitaxial growth of narrow gap dilute nitride InAsN alloys onto GaAs substrates using a nitrogen plasma source. The photoluminescence (PL) of InAsN alloys with N-content in the range 0 to 1% which exhibit emission in the mid-infrared spectral range is described. The sample containing 1% N reveals evidence of recombination from extended and localized states within the degenerate conduction band of InAsN. A comparison of GaAs and InAs based material shows little change in PL linewidth such that the change in substrate does not cause significant reduction in quality of the epilayers. The band gap dependence on N content in our material is consistent with predictions from the band anti-crossing model. We also report the growth of InAsSbN/InAs multi-quantum wells which exhibit bright PL up to a temperature of 250 K without any post growth annealing. Consideration of the power dependent PL behaviour is consistent with Type I band alignment arising from strong lowering of the conduction band edge due to N-induced band anti-crossing effects.

The air quality of any manned spacecraft needs to be continuously monitored in order to safeguard the health of the crew. Air quality monitoring grows in importance as mission duration increases. Due to the small size, low power draw, and performance reliability, semiconductor laser-based instruments are viable candidates for this purpose. Achieving a minimum instrument size requires lasers with emission wavelength coinciding with the absorption of the fundamental absorption lines of the target gases, which are mostly in the 3.0-5.0 μm wavelength range. In this paper we report on our progress developing high wall plug efficiency type-I quantum-well GaSb-based diode lasers operating at room temperatures in the spectral region near 3.0-3.5 μm and quantum cascade (QC) lasers in the 4.0-5.0 μm range. These lasers will enable the development of miniature, low-power laser spectrometers for environmental monitoring of the spacecraft.

A review of applications for tunable diode laser spectroscopy (TDLS) instrumentation in process analytics is presented. We have investigated applications in olefin production suitable for TDLS instrumentation. The possibility to detect acetylene impurities in different hydrocarbon backgrounds was investigated by TDLS in the 3 micron wavelength region using novel GaInAsSb/AlGaAsSb DFB lasers. The performance of the TDLS instrument for detection of acetylene impurities in pure ethylene and in a gas matrix typical of a hydrogenating reactor was investigated more in detail. Experiments with in-situ measurements of hydrocarbons in an industrial environment using a modified Siemens TDLS instrument are also discussed.

Faraday Rotation Spectroscopy (FRS) is a technique for the sensitive and selective detection of paramagnetic molecules or radicals such as NO, NO₂, O₂ or OH^-. Moreover FRS is suitable for atmospheric measurements due to the insensitivity to non-paramagnetic interfering molecules such as H₂O and CO₂. Experimental results of an FRS sensor for the NO₂detection employing an external-cavity quantum cascade laser (EC-QCL) are reported. The CW EC-QCL exhibits modehop free (MHF) tuning between 1600 cm^-1 and 1650 cm^-1. This allows targeting the optimum 4₄₁←4₄₀ Q-branch NO₂transition at 1613.25 cm^-1. A rotation of the polarization state of the initially linearly polarized laser light is observed when an AC magnetic field is applied to the NO₂ cell, placed between two nearly crossed Rochon polarizers. This rotation of the polarization state is proportional to the NO₂ concentration and can be determined by a photodetector located after the second polarizer. For long-term continuous measurements a second branch consisting of a detector and reference cell filled with 0.2 % NO₂ in N₂ is used to lock the laser to the selected NO₂ transition. A minimum detection sensitivity (1σ) of 1 parts per billion (ppbv) was obtained for a 1 sec lock-in time constant (TC).

We present a system for the stand-off detection of solid explosive traces and precursors on surfaces. The system consists of a widely tunable quantum cascade laser (QCL) and a thermal imaging camera. The external cavity quantum cascade laser (EC-QCL) illuminates the surface of a distant object at different characteristic wavelengths. In synchronisation with the camera a hyperspectral data cube of the backscattered radiation is generated allowing a multivariate analysis of the scene. We demonstrate how multidimensional image processing is used in order to fast and sensitively detect traces of hazardous substances such as trinitrotoluene (TNT) or pentaerythritol tetranitrate (PETN). The recognition algorithm is developed to effectively suppress false alarms. Experiments are performed on real world like surfaces such as standard car paint, synthetic cloth or jeans fabric.

Optothermal detection is a spectroscopic technique where the energy input into a gas or other media caused by absorption of optical radiation is measured directly by means of a thermal detector._1-3 A fraction of the absorbed energy is transported to the thermal detector by heat conduction or molecular diffusion. In this work a conventional thermal sensor was replaced by a quartz tuning fork (QTF), and the optical power input into the gas was modulated at the QTF resonant frequency. We call this approach "resonant optothermoacoustic detection", or ROTADE. The same experimental setup can be used to conduct a closely related technique, quartz enhanced photoacoustic spectroscopy (QEPAS).⁴ QEPAS relies on energy transfer from the initially excited molecular vibrational state to the translational degrees of freedom. In some cases this process is too slow to follow the modulation required for QEPAS. In other cases, the resonant energy transfer can result in vibrational excitation of nitrogen, which relaxes very slowly. ROTADE, on the other hand, detects the energy delivered by molecules even if this energy is still in the form of vibrational excitation. The molecules will then release their energy to the QTF upon collision with its surface. Experimental investigations of ROTADE and its comparison with QEPAS were performed in pure CO2 and 0.5% acetylene in N² using near-infrared diode lasers. A fiber collimator and a refocusing lens were used to focus the laser to a ≈15 μm diameter waist. Its position was scanned in the QTF plane using a 3D translation stage with computer-controlled actuators. Different QTFs were used to compare the effect of modulation frequency on the ROTADE signal.

A quartz-enhanced photoacoustic spectroscopy (QEPAS) based multi-gas sensor was developed to quantify concentrations of carbon monoxide (CO), hydrogen cyanide (HCN), hydrogen chloride (HCl), and carbon dioxide (CO₂) in ambient air. The sensor consists of a compact package of dimensions 25cm x 25cm x 10cm and was designed to operate at atmospheric pressure. The HCN, CO₂, and HCl measurement channels are based on cw, C-band telecommunication-style packaged, fiber-coupled diode lasers, while the CO channel uses a TO can-packaged Sb diode laser as an excitation source. Moreover, the sensor incorporates rechargeable batteries and can operate on batteries for at least 8 hours. It can also operate autonomously or interact with another device (such as a computer) via a RS232 serial port. Trace gas detection limits of 7.74ppm at 4288.29cm^-1 for CO, 450ppb at 6539.11 cm^-1 for HCN, 1.48ppm at 5739.26 cm^-1 for HCl and 97ppm at 6361.25 cm^-1 for CO₂ for a 1sec average time, were demonstrated.

The air quality of any manned spacecraft needs to be continuously monitored in order to safeguard the health of the crew. Any fire event, accidental release of harmful gaseous contaminants or a malfunction in the air revitalization system has to be detected as fast as possible to provide enough time for the crew to react. In this paper, a fast sensor system based on laser spectroscopy is presented, which is able to detect three important gases: carbon monoxide for fire detection, hydrogen chloride for fire characterization and oxygen to monitor the air vitalization system. To provide a long maintenance-free operation time without the need for any consumables except power, a calibration-free measurement method was developed, which is only based on molecule specific constants which are available from the molecular data base HITRAN. The presented sensor offers the possibility for reliable and crosssensitivity-free air quality monitoring over a large pressure and temperature range.

In this paper we investigate the possibility of producing local population inversion that can lead to lasing without inversion by engineering the conduction band effective masses in dilute nitride structures so that the upper lasing subband has an effective mass considerably smaller than the lower lasing subband that could not be obtained in usual IIIV materials. This analysis is the first step towards possible far infrared dilute nitride based quantum cascade lasers that could benefit from the gain without inversion effect to operate at higher temperatures.

Imaging arrays of direct detectors in the 0.5-5 THz range are being experimentally developed. Terahertz active imaging with amplitude-modulated quantum cascade lasers emitting at 2.5 and 4.4 THz performed by using an antenna-coupled superconducting microbolometer. We then present two room-temperature terahertz detector technologies compatible with monolithic arrays: i) GaAs Schottky diodes with air-bridge sub-micron anodes; ii) high electron mobility transistors with sub-micron Schottky gate. Performances, requirements and fabrication costs of the different detector technologies are compared.

We present a numerical and experimental study of the dispersion relation and propagation properties of bound surface waves on a meta-surface consisting of a single layer array of split ring resonators. Furthermore, we introduce an analytic model that allows one to determine the influence of nonlinear effects on the temporal dynamics of a coupled system composed of a split ring resonator metamaterial and a two-level atomic gain medium.

Electronic transport in AlGaAs/GaAs THz Quantum Wells Intersubband Photodetectors (QWIPs) exhibits two different regimes separated by huge discontinuities (up to five orders of magnitude) in the resistivity. They are interpreted in terms of band structure reorganizations triggered by intersubband impact ionization. We will analyze and model their in uence on the electronic transport. The magnitude of the transport modifications is explained by the small transition energy and the sharpness of the electrons distribution at stake in THz QWIPs. Measurements under magnetic field or temperature show that the broadening of the electron distribution damps the effects of impact ionization. Some experimental features of the electronic transport of shorter wavelength detectors are then reproduced. The use of intersubband impact ionization in THz QWIPs to design high gain and fast novel detectors is discussed.

Thanks to the modern compound semiconductor growth and processing technologies, quantum wells and related semiconductor nanostructures have been widely investigated for infrared-terahertz devices. Here we propose a new general approach to make use of polar optical phonons in quantum wells for infrared (IR) and terahertz (THz) detection. Polar optical phonons strongly couple with both electrons and photons, and hence are potentially useful for photonic devices. As the first example, we show the coupling of phonon and intersubband transition leading to Fano resonance in photocurrent spectra. We investigate the phenomenon experimentally in specially designed GaAs/AlGaAs quantum well infrared photodetectors. Finally, we discuss the future research and potentials. Strongly coupled systems of electrons and phonons, i.e., polarons, may lead to new IR-THz photodetectors.

In this work we investigate two different approaches to generate THz radiation by the use of the unique electrical and thermal properties of GaN. One method is heterodyne photomixing, a compact and inexpensive approach to generate continuous electromagnetic radiation in the terahertz range, with tuneable frequency. It uses two lasers with slightly different wavelengths that illuminate an ultrafast photoconductor. The interference of both laser beams generates a beat frequency of the illumination intensity in the terahertz range. One drawback of the conventionally used LT GaAs as ultrafast photoconductor material is the relatively low THz power in the nW to μW range. The aim of our work is to increase the output power by replacing the LT GaAs with GaN. This semiconductor is rather known as basic material for blue LEDs and lasers, but it has also remarkable electrical and thermal properties that allow higher laser power and bias voltage. A more conventional, electronic approach to generate THz radiation consists in the fabrication of an oscillator circuit based on ultrafast transistors, e.g. Hetero Field Effect Transistors based on InGaAs. These circuits can be designed up to about 100 GHz oscillation frequency. The THz region is achieved by frequency multipliers, e.g. realized by very small-sized Schottky diodes. However, each multiplier stage considerable reduces the output power. In this field we investigate GaN based transistor devices to profit from the much better power performance of this material, compared to classical semiconductors. Devices in this material system are usually used for high power applications at moderate frequencies, but the very high electron saturation velocity of GaN allows the application above 100 GHz as well.

We report terahertz (THz) emission from magnesium doped a-plane indium nitride (a-InN:Mg) films with different background carrier density, relative to the Mg-doped InN films grown along the c-axis (c-InN:Mg). Due to its high electron affinity, as-grown InN film is typically n-type and it has extremely high background carrier density, which causes much weaker THz emission than that from other semiconductors, such as InAs. The background carrier density of Mg-doped InN can be widely changed by adjusting the Mg doping level. For c-InN:Mg, THz emission is dramatically enhanced (×500 than that of undoped c-InN) as the background carrier density decreases to a critical value of ~1×10¹⁸cm^-3, which is due to the reduced screening of the photo-Dember field at the lower carrier density. For a-InN, however, intense THz emission (×400 than that of undoped c-InN) is observed for both undoped and Mg-doped a-InN and the enhancement is weakly dependent on the background carrier density. The primary THz radiation mechanism of the aplane InN film is found to be due to the acceleration of photoexcited carriers under the polarization-induced in-plane electric field perpendicular to the a-axis, which effectively enhances the geometrical coupling of the radiation out of semiconductor. The weak dependence of THz radiation on the background carrier density for a-InN shows that in-plane surface field induced-terahertz emission is not affected by the background carrier density. Small, but apparent azimuthal angle dependence of terahertz emission is also observed for a-InN, indicating the additional contribution of nonlinear optical processes on terahertz emission.

We investigated the surface plasmon coupling behavior in InGaN/GaN multiple quantum wells at 460 nm by employing Ag nanostructures on the top of a roughened p-type GaN. After the growth of a blue light emitting diode structure, the p-GaN layer was roughened by inductive coupled plasma etching and the Ag nanostructures were formed on it. This structure showed a drastic enhancement in photoluminescence and electroluminescence intensity and the degree of enhancement was found to depend on the morphology of Ag nanostructures. From the time-resolved photoluminescence measurement a faster decay rate for the Ag-coated structure was observed. The calculated Purcell enhancement factor indicated that the improved luminescence intensity was attributed to the energy transfer from electron-hole pair recombination in the quantum well to electron vibrations of surface plasmon at the Ag-coated surface of the roughened p-GaN.

Plasmonic has demonstrated the ability to enhance performances of photodetectors at a resonant wavelength. Absorption in a photodetector can reach 100% using nanophotonic plasmonic array. Plasmonic devices are confining light at the interface metal/dielectric, as a consequence, detection volume is smaller (100 to 1000 times) than in usual photodetectors leading to a decrease in dark current of infrared photodetectors and therefore a higher working temperature. The second consequence of a short detection volume is a higher collection efficiency of photocarriers as the transit time is smaller than the lifetime.

Surface plasmons polaritons are electromagnetic waves propagating along the surface of a conductor. Surface plasmons photonics is a promising candidate to satisfy the constraints of miniaturization of optical interconnects. This contribution reviews an experimental parametric study of dielectric loaded surface plasmon waveguides ring resonators and add-drop filters within the perspective of the recently suggested hybrid technology merging plasmonic and silicon photonics on a single board (European FP7 project PLATON "Merging Plasmonic and Silicon Photonics Technology towards Tb/s routing in optical interconnects"). Conclusions relevant for dielectric loaded surface plasmon switches to be integrated in silicon photonic circuitry will be drawn. They rely on the opportunity offered by plasmonic circuitry to carry optical signals and electric currents through the same thin metal circuitry. The heating of the dielectric loading by the electric current enables to design low foot-print thermo-optical switches driving the optical signal flow.

It is discussed how to measure the radiation of the cold Universe using the transient photoresponse of space IR detectors. This approach, which is based on the theory of transients in extrinsic photoconductors, permits to substantially improve the precision of the measurements. This has been specifically confirmed by the treatment of the data of the ISOCAM space detectors. The success of the treatment increases with the increase of the quality of the detectors and their contacts.

The growth and characterization of some cubic III-nitride films on suitable cubic substrates have been done, namely, c- GaN on GaAs by MOVPE, c-GaN and c-AlGaN on MgO by RF-MBE, and c-InN and c-InGaN (In-rich) on YSZ by RFMBE. This series of study has been much focused on the cubic-phase purity as dependent on the respective growth conditions and resulting electrical and optical properties. For c-GaN and c-InN films, a cubic-phase purity higher than 95% is attained in spite of the metastable nature of the cubic III-nitrides. However, for c-AlGaN and c-InGaN films, the cubic-phase purity is rapidly degraded with significant incorporation of the hexagonal phase through stacking faults on cubic {111} faces which may be exposed on the roughened growing or substrate surface. It has been shown that the electron mobilities in c-GaN and c-AlGaN films are much related to phase purity.

In this work, the detailed MOVPE growth properties of InAsN films with N contents up to 2.54% and the photoluminescence properties in relation with the carrier concentrations were investigated. For the MOVPE growth, tertiary-butylarsine (TBAs) and 1,1-dimethylhydrazine (DMHy) were used as the group-V precursors. The efficient growth conditions for the InAsN films with higher N contents are a higher DMHy/V ratio and a lower As/In ratio. The photoluminescence emission from the post-annealed InAsN films exhibits a blue-shift with increasing the N content, which is contrary to the expected bandgap bowing. The same blue-shift behavior was observed in InAsN films grown on SI-GaAs(001) substrate by RF-MBE. As a result of temperature dependent photoluminescence measurements under various excitation powers, it was found that the blue-shift of the PL-peak energy of the InAsN films was attributed to the band-filling effect due to the degenerate electrons induced by the N incorporation.

To promote the research on the growth of high-quality InN films attractive to the application for both optical and electronic devices, the pressurized-reactor metalorganic-vapor-phase epitaxy (PR-MOVPE) system which can overcome the high equilibrium-vapor-pressure of nitrogen between solid and vapor phases is originally developed. In addition to this system, the N-polar growth technique developed in the growth of GaN is introduced. As a result, the dense InN films with atomic steps are successfully grown. From the struggle of the research on high quality InN, the subject of the phase purity is also arisen. The pole figure measurements make the growth condition for a pure InN with a wurtzite structure. The phase purity is almost determined by the growth temperature. These results will pave the way to high-quality InN.

Al(Ga)N/GaN resonant tunneling diodes (RTDs) are grown by metal-organic chemical vapor deposition. The effects of material quality on room temperature negative differential resistance (NDR) behaviour of RTDs are investigated by growing the RTD structure on AlN, GaN, and lateral epitaxial overgrowth GaN templates. This reveals that NDR characteristics of RTDs are very sensitive to material quality (such as surface roughness and dislocations density). The effects of the aluminum content of AlGaN double barriers (DB) and polarization fields on NDR characteristic of AlGaN/GaN RTDs were also investigated by employing low dislocation density c-plane (polar) and m-plane (nonpolar) freestanding GaN substrates. Lower aluminum content in the DB RTD active layer and minimization of dislocations and polarization fields enabled a more reliable and reproducible NDR behaviour at room temperature.

Various types of nano-to-micron scale patterned structure have been employed into nitride light-emitting diodes (LEDs) in order to investigate the optical performances of device. The patterned structure was formed on top of the LED epitaxial structure or was embedded between epitaxial layers and sapphire substrate. The patterned structure affected to the LED performances in terms of light distribution and anisotropic increase of light extraction as well as increase of external quantum efficiency. The controllability of light extraction by forming a patterned structure with different index material is applicable to flip chip devices or chips on board in which light is supposed to be extracted toward a certain direction with the straight forward directionality. The index matched nano-patterned AlN template played such a role of anisotropic directionality of light extraction in the device. Periodic (photonic band gap) and non-periodic (random hole) patterned structure also showed different extraction efficiency and characteristics of light distribution. The experimental result was well matched with the simulated estimation.

Extending the intersubband transitions in III-nitride nanostructures from near-infrared to longer wavelengths might have significant consequences for critical applications like imaging, remote sensing and mine detection. In this work, we analyze the potential of polar AlGaN/GaN heterostructures for this relevant spectral range.

The electron microscope provides a wide range of techniques that are very well suited for structural characterization of nanophotonic materials and devices. High-resolution electron microscopy (defect identification and strain field analysis), Z-contrast imaging in the scanning transmission electron microscope (cation distribution), convergent-beam electron diffraction (local lattice parameter and strain), and off-axis electron holography (internal electrostatic fields), represent powerful complementary approaches for distinguishing between the often-competing effects of growth conditions and compositional differences. These various TEM techniques have been used separately or in tandem in our recent collaborative studies of III-nitride heterostructures and nanostructures, where lattice mismatch, compositional inhomogeneities and phase separation were all important considerations that can possibly impair the structural quality of the final material and/or device. Representative applications that illustrate the prospects and some of the problems include the following: i) relaxed InN quantum dots; ii) deep-UV-emitting AlGaN quantum wells; iii) near-UV light-emitting diodes based on InN/GaN quantum wells; and iv) blue-green LEDs based on GaN quantum-dot superlattices.

Properties of GaN radiation detectors are analyzed. It is shown that present day epitaxial material is suitable for detection of α-particles with the charge collection efficiency close to 100%. Such detectors can operate at temperatures of at least 60°C and withstand irradiation with reactor neutrons fluences higher than 1015 cm^-2. They keep the collection efficiency at 30% even after irradiation with 2×1016 cm^-2 neutron fluence. Registration of thermal neutrons with GaN detectors can also be achieved by using ¹⁰B converter and the efficiency of registration is determined by the ¹⁰B conversion efficiency from neutrons to low energy a-particles.

In this paper, we describe our current state-of-the-art process of making visible-blind APDs based on GaN. We have grown our material on both conventional sapphire and low dislocation density free-standing c- and m-plane GaN substrates. Leakage current, gain, and single photon detection efficiency (SPDE) of these APDs are compared. The spectral response and Geiger-mode photon counting performance of UV APDs are studied under low photon fluxes. Single photon detection capabilities with over 30% are demonstrated. We show how with pulse height discrimination the Geiger-mode operation conditions can be optimized for enhanced SPDE versus dark counts.

Mid-wavelength infrared (MWIR) InAs/GaSb superlattice (SL) pin photodiodes were fabricated by molecular Beam Epitaxy on p-type GaSb substrate. Dark current measurements as a function of temperature were performed on single SL detectors with two different period designs: one made of standard symmetric 8 InAs monolayers (MLs) / 8 GaSb MLs SL period, another made of alternative design with asymmetric 7.5 InAs MLs / 3.5 GaSb MLs SL period. Comparison of results revealed the predominance of the asymmetric SL design showing an improvement of the differential resistance area product of nearly two orders of magnitude. Spectral response measurements performed on asymmetric SL showed that the quantum efficiency was more than doubled.

Split-off band detectors have been demonstrated operating at or above room temperatures. However the specific detectivity was somewhat low due to the high dark current. Increasing the barrier height can suppress the dark current at high temperatures but results in a low responsivity due to the capture of carriers in emitters. A difference between the heights of the barriers on the two sides of an emitter provides highly energized carriers injected into the emitter and hence reduces the trapping effects. Three p-GaAs/AlGaAs samples with different Al fractions in the graded barriers are used to test these effects. Due to the graded barrier, the samples have an asymmetric band structure which makes it easier for excited carriers to travel in one direction than in the other. Therefore, photovoltaic operation is possible due to the built-in potential under equilibrium. Preliminary results obtained from these samples will be discussed.

At the Air Force Research Laboratory's Space Vehicles Directorate, we are investigating how nanostructured metal surfaces can produce plasmon-enhanced fields to improve detectivity of a detector material placed directly below the metal surface. We are also investigating a wavelength-tunable detector scheme that involves a coupled double quantum well structure with a thin middle barrier between the two wells. The photocurrent from this structure will be swept out with a lateral bias. Another form of wavelength tunability is to have a tunable filter in front of a broadband detector. There are many avenues of research that lead to such a device. The way we are approaching this is via the new field of metamaterials. Not only might these new materials present us a way to tune the light that is incident upon a detector, but such research might also lead to ways to obtain sub-diffraction-limit resolution and the concentration of light using flat lenses for increased signal-to-noise ratios. In this talk we will discuss the research efforts being pursued in the above areas.

Mid-infrared spectroscopy has gained significant importance in recent years as a detection technique for substances that absorb in this spectral region. Traditionally, a spectroscopic system consists of bulky equipment which is difficult to handle and incurs high cost. An integrated spectroscopic system would eliminate these disadvantages. GaSb-based active opto-electronic devices allow realizing mid-infrared light sources and detectors in the 2-3μm wavelength range for such integrated systems. Silicon photonics, based on Silicon-on-Insulator (SOI) waveguide circuits, on the other hand, is a well established technology based on high refractive index contrast waveguides, enabling ultra-compact passive integrated photonic circuits. Moreover, SOI waveguide circuit processing is compatible with CMOS processes. Hence, the integration of GaSb-based active devices onto SOI passive waveguide circuits potentially allows highly compact spectroscopic systems with a large degree of freedom in passive device design to improve the system performance. This approach has a high potential for several applications, e.g. an implantable glucose level monitor and gas sensing devices. In this paper, we report our work on the integration of GaSb-based epitaxy onto SOI waveguide circuits. The heterogeneous integration is based on an epitaxial layer transfer process using the polymer divinylsiloxanebenzocyclobutene (DVS-BCB) as a bonding agent. The process is performed by transferring the epitaxial layer to an SOI waveguide circuit wafer through a die-to-wafer bonding process. With this approach, a bonding layer of 150 nm thickness is easily achievable. We also report our results on the integration of waveguide-based GaSb p-i-n photodetectors coupled to SOI waveguide circuits using evanescent coupling, which show a responsivity higher than 0.4A/W. The design of active and passive structures and the overall fabrication process will also be discussed.

A nearly universal goal for infrared photon detection systems is to increase their operating temperature without sacrificing performance. For high quality HgCdTe photovoltaic infrared detectors at elevated temperatures, the lowdoped absorber layer becomes intrinsic, carrier concentrations are high and Auger processes typically dominate the dark current. Device designs have been proposed to suppress Auger processes in the absorber by placing it between exclusion and extraction junctions under reverse bias. In this work, we analyze the non-equilibrium operation of very long wavelength infrared (VLWIR) HgCdTe devices and identify the performance improvements (operation temperature, responsivity, detectivity) expected when Auger suppression occurs. We identify critical structure design requirements that must be satisfied for optimal performance characteristics from VLWIR non-equilibrium devices and compare these devices with current state of the art double layer planar heterostructure (DLPH) devices.

InAs/GaSb short-period superlattices (SL) have proven their large potential for high performance focal plane array infrared detectors. Lots of interest is focused on the development of short-period InAs/GaSb SLs for mono- and bispectral infrared detectors between 3 - 30 μm. InAs/GaSb short-period superlattices can be fabricated with up to 1000 periods in the intrinsic region without revealing diffusion limited behavior. This enables the fabrication of InAs/GaSb SL camera systems with very high responsivity, comparable to state of the art CdHgTe and InSb detectors. The material system is also well suited for the fabrication of dual-color mid-wavelength infrared InAs/GaSb SL camera systems. These systems exhibit high quantum efficiency and offer simultaneous and spatially coincident detection in both spectral channels. An essential point for the performance of two-dimensional focal plane infrared detectors in camera systems is the number of defective pixel on the matrix detector. Sources for pixel outages are manifold and might be caused by the dislocation in the substrate, the epitaxial growth process or by imperfections during the focal plane array fabrication process. The goal is to grow defect-free epitaxial layers on a dislocation free large area GaSb substrate. Permanent improvement of the substrate quality and the development of techniques to monitor the substrate quality are of particular importance. To examine the crystalline quality of 3" and 4" GaSb substrates, synchrotron white beam X-ray topography (SWBXRT) was employed. In a comparative defect study of different 3" GaSb and 4" GaSb substrates, a significant reduction of the dislocation density caused by improvements in bulk crystal growth has been obtained. Optical characterization techniques for defect characterization after MBE growth are employed to correlate epitaxially grown defects with the detector performance after hybridization with the read-out integrated circuit.

One of the great advantages of Type II InAs/GaSb superlattice over other competing technologies for the third generation infrared imagers is the potential to have excellent uniformity across a large area as the electronic structure of the material is controlled by the layer thicknesses, not by the composition of the materials. This can economize the material growth, reduce the fabrication cost, and especially allow the realization of large format imagers. In this talk, we report the molecular beam epitaxial growth of Type II superlattices on a 3" GaSb substrate for long wavelength infrared detection. The material exhibits excellent structural, optical and electrical uniformity via AFM, Xray, quantum efficiency and I-V measurements. At 77K, 11μm cutoff photodiodes exhibit more than 45% quantum efficiency, and a dark current density of 1.0x10^-4A/cm² at 50 mV, resulting in a specific detectivity of 6x10¹¹ cm.Hz^1/2/W.

The nearly lattice-matched InAs/GaSb/AlSb (antimonide) material system offers tremendous flexibility in realizing high-performance infrared detectors. Antimonide-based superlattice (SL) detectors can be tailor-made to have cutoff wavelengths ranging from the short wave infrared (SWIR) to the very long wave infrared (VLWIR). SL detectors are predicted to have suppressed Auger recombination rates and low interband tunneling, resulting in the suppressed dark currents. Moreover, the nearly lattice-matched antimonide material system, consisting of InAs, GaSb, AlSb and their alloys, allows for the construction of superlattice heterostructures. In particular, unipolar barriers, which blocks one carrier type without impeding the flow of the other, have been implemented in the design of SL photodetectors to realize complex heterodiodes with improved performance. Here, we report our recent efforts in achieving state-of-the-art performance in antimonide superlattice based infrared photodetectors.

We report on the investigation of lateral diffusion of minority carriers in InAsSb based photodetectors with the nBn design. Diffusion lengths (DL) were extracted from temperature dependent I-V measurements. The behavior of DL as a function of applied bias, temperature, and composition of the barrier layer was investigated. The obtained results suggest that lateral diffusion of minority carriers is not the limiting factor for InAsSb based nBn MWIR detector performance at high temperatures (> 200K). The detector with an As mole fraction of 10% in the barrier layer has demonstrated values of DL as low as 7 μm (V_b = 0.05V) at 240K.

IR detectors operated in a space environment are subjected to a variety of radiation effects while required to have very low noise performance. When properly passivated, conventional mercury cadmium telluride (MCT)-based infrared detectors have been shown to perform well in space environments. However, the inherent manufacturing difficulties associated with the growth of MCT has resulted in a research thrust into alternative detector technologies, specifically type-II Strained Layer Superlattice (SLS) infrared detectors. Theory predicts that SLS-based detector technologies have the potential of offering several advantages over MCT detectors including lower dark currents and higher operating temperatures. Experimentally, however, it has been found that both p-on-n and n-on-p SLS detectors have larger dark current densities than MCT-based detectors. An emerging detector architecture, complementary to SLS-technology and hence forth referred to here as nBn, mitigates this issue via a uni-polar barrier design which effectively blocks majority carrier conduction thereby reducing dark current to more acceptable levels. Little work has been done to characterize nBn IR detectors tolerance to radiation effects. Here, the effects of gamma-ray radiation on an nBn SLS detector are considered. The nBn IR detector under test was grown by solid source molecular beam epitaxy and is composed of an InAs/GaSb SLS absorber (n) and contact (n) and an AlxGa1-xSb barrier (B). The radiation effects on the detector are characterized by dark current density measurements as a function of bias, device perimeter-to-area ratio and total ionizing dose (TID).

Low dark current and high fill factor are two crucial characteristics for the realization of the InAs/GaSb superlattice (SL) technology as third generation focal plane arrays (FPAs). Recent development proved high performance results for the complementary barrier infrared detector (CBIRD) design, and a high-quality etch technique is required to minimize surface leakage currents. We report on a n-CBIRD with 10.3 μm cutoff, exhibiting a responsivity of 1.7 A/W and dark current density of 1×10^-5 A/cm² at 77K under 0.2 V bias, without AR coating and without passivation. Results from four different mesa isolation techniques are compared on single element diodes: chemical wet etch using C₄H₆O₆:H₃PO₄:H₂O₂:H₂O, BCl₃/Ar inductively coupled plasma (ICP), CH4/H2/Ar ICP, and CH₄/H₂/BCl₃/Cl₂/Ar ICP. The CH₄/H₂/BCl₃/Cl₂/Ar etched structures yielded more than 2.5 times improvement in dark current density and nearvertical sidewalls. Using this etching technique, we then implement a 1k x 1k p-CBIRD array with 11.5 μm cutoff and peak responsivity of 3 A/W. Operating at T = 80K, the array yielded a 81% fill factor with 98% operability and performance results of 21% quantum efficiency, 53 mK NE▵T, and NEI of 6.9×10¹³ photons/sec-cm².

Operation of InAs/GaSb superlattice-based devices requires efficient transport of carriers perpendicular to superlattice layers by drift and/or diffusion. While transverse mobility measurements are performed routinely, vertical transport measurements are difficult and nonstandard, so that very little is known about their value and dependence on material quality, which is important in device modeling. In such a situation, model calculations can help fill the void. In this work, both the horizontal and vertical electron transport in InAs/GaSb superlattices qua superlattices, not quantum wells, as in Gold's model or its extensions, are modeled. The respective Boltzmann equations in the relaxation time approximation are solved, using the interface roughness scattering as the dominant mobility-limiting mechanism. In absence of screening, a universal relation that the vertical relaxation rates are always smaller than horizontal relaxation rates is derived; hence vertical mobilities are generally smaller than horizontal mobilities. We calculate vertical and horizontal mobilities as a function of such superlattice parameters as layer widths and the correlation length of interface roughness. The calculated ratios of the vertical to horizontal mobilities can be used to estimate vertical mobilities from measurements of horizontal mobilities.

In this paper, we demonstrate a high operating temperature (HOT) quantum dot-in-a-well (DWELL) infrared photodetector with enhanced normal incidence (s-polarization) radiation photocurrent. The s-to-p polarization ratio was increased to 50%, compared to the 20% in conventional quantum dot detectors. This improvement was achieved through engineering the dot geometry and the quantum confinement via post growth capping materials of the quantum dots (QDs). The effect of the capping procedures was determined by examining the dot geometry using transmission electron microscopy (TEM) and s-to-p polarization induced photocurrent in the DWELL structure photodetector. The TEM image shows a quantum dot with a reduced base of 12 nm and an increased height of 8 nm. The infrared photodetectors fabricated from this material shows a peak photodetectivity of 1×10⁹ cmHz^1/2/W at 77K for a peak wavelength of 4.8 μm and 1×107 cmHz^1/2/W at 300K for a peak wavelength of 3.2 μm. The dark current density is as low as 2×10^-4A/cm² and the photocurrent gain is 100 at the optimal operating bias.

In order to be commercially viable, the type-II superlattice (T2SL) LWIR focal plane array technology will require the development of effective passivation of exposed surfaces. Here we investigate the relationship between the thickness and composition of the native oxide at the T2SL-SiO₂ interface and the diode performance in terms of sidewall resistivity. Device performance is compared between samples with untreated surfaces, those for which the native oxides have been removed at various intervals prior to SiO₂ deposition, and samples for which oxide growth was promoted by ozone exposure with and without a prior oxide strip. InAs- and GaSb-capped pieces were processed in an identical manner and studied using X-ray photoelectron spectroscopy (XPS). From these spectra, the compositions and thicknesses of the surface oxides just prior to SiO₂ deposition were determined, complementing the electrical characterization of devices. Correlation of the performance and surface composition is presented.

We investigate in this paper the potential of carbon nanotubes for infrared bolometers. A method to obtain CNT film layer and technological processes to obtain matrix of devices are presented. The electrical characterization of samples establishes the quality of our technology i.e. low contact resistance, and weak dispersion between devices. The potential of carbon nanotubes films as bolometric material is investigated by measuring the thermal dependence of their resistance and by comparison with amorphous silicon (one of the leading material for bolometric applications). Optical measurements of CNT films in the infrared and THz ranges show a relatively high absorption for a few hundreds nanometers thick material. Eventually the infrared (8-12 μm) photo-response of a first demonstrator is presented and discussed.

In this work, the results are presented of a nanorod LED array. If the lateral size of the nanorods is small enough, it is possible to achieve a degree of lateral confinement. If the nanorods are ordered into a suitable photonic lattice, then this will reduce the lateral spontaneous emission and enhance emission along the vertical axis via the Purcell effect. Additionally there is a degree of dislocation filtering that can occur [1]. However, one potential drawback of this device is the large free surface that borders the multi-quantum well active region. Nevertheless, it has been shown that the surface recombination in the nitride materials is the lowest of all III-V semiconductors. Results of SEM, PL, EL, and far field pattern are presented to compare the progressive effect of using photo-assisted electroless and wet etching [2]. It can be seen that over time the photo-assisted electroless method clearly delineates the active MQW region, possibly as a result of the different etch rate of InGaN. Alternatively, a purely chemical etching method was used. With a narrowing of the nanorods, there is a progressive blue shift of the photoluminescence peak. The optical image of the emission shows that there are well-defined lines of enhanced light propagation that match the symmetry of the nanorod array, thus showing there is a photonic crystal effect.

High density arrays of nanostructures over large area can be formed by self-assembly of block copolymers on a variety of substrates such as silica deposited silicon wafer, glass, GaN, PET etc. This block copolymer thin film, such that the domains are oriented perpendicularly to the substrate, is particularly useful for the formation of templates for patterns. The degradation and elimination of the minor component transforms the material into an array of nanopores to form some patterned template that offer potential benefits in a number of applications. The morphology of the polymer surface is strongly dependent on the thickness of the polymer layer. Moreover it is necessary to control the size and shape in order to get the desired properties. Spin coating fallowed by baking the polymer solution onto the substrate self assembles the components of the polymer. PS and PMMA have significantly different photodegradation properties. Exposure to ultraviolet radiation degrades the PMMA (polymethyl methacrylate) chain that can be removed by rinsing in acetic acid giving patterned holes. Sonicating the samples in different solutions in different steps gives fingerprint pattern or sometimes patterns with PS cylindrical domains with large interstitial spaces. Moreover the interstitial space depends on the composition of the polymer solution. All these controlled patterns made on GaN, Glass can be applied to make photonic crystal

Here we report a flexible piezoelectric nanodevices (nanogenerators) that can be utilized as both a touch sensor and a light sensor on a single platform. Based on the electron transporting and piezoelectric properties of ZnO, nanogenerators with a ZnO/conjugated polymer stacked structure was designed on a plastic substrate. Piezoelectric touch signals were demonstrated under independent and simultaneous operations with respect to photo-induced charges (photodetection). Different levels of piezoelectric output signals from different magnitude of touching pressures suggest new user-interface functions from our hybrid nanogenerators. From a signal controller, the decoupled performance of a hybrid nanogenerator as a touch sensor and a light sensor was confirmed. Our hybrid approach does not require additional assembling processes for such multiplex systems of a touch sensor and a light sensor since we utilize the coupled material properties of ZnO and output signal processing. Moreover, it should be noted that the hybrid nanogenerator can be operated in a self-powered mode without any power supply.

We study theoretically and experimentally the IR emission properties from gold nano-antenna arrays. A new characterization method based on far field measurements only is developed and presented. Excellent agreement in terms of resonance frequencies, optical bandwidth, and emission efficiency is found between the experimental results and a theoretical analysis based on finite element modeling of the arrays. Extremely high overall emission efficiencies, exceeding 95%, are obtained experimentally. The high efficiency and the simple far-field characterization scheme presented here can facilitate the employment of such nano-antennas for numerous applications in imaging, spectroscopy, and solar energy harvesting.

In this paper, we review the design, processing, and characterization of novel planar infrared chemical sensors. Chalcogenide glasses are identified as the material of choice for sensing given their wide infrared transparency as well as almost unlimited capacity for composition alloying and property tailoring. Three generations of on-chip spectroscopic chemical sensor devices we have developed: waveguide evanescent sensors, micro-disk cavity-enhanced sensors and micro-cavity photothermal sensors are discussed.

A microring resonator is used as a photonic sensor device for the detection of the explosive trinitrotoluene (TNT). Selectivity is achieved by coating the sensor chip with specially designed receptor molecules. The measurand is the shift in resonance frequency of the microring resonator induced by the change in effective index of refraction of the waveguide materials due to adsorption/intercalation of the analyte. The response is linear with concentration and reversible, i.e. the TNT molecules desorb from the sensor surface when it is flushed with carrier gas. This enables online measurements since the sensor can be used again after flushing and no sampling is needed. Insensitivity to other substances is demonstrated. Some chemically similar molecules induce a shift also, but the sensitivity is much lower. The sensing limit for TNT is determined to be 0.5ppb. Simultaneous operation of two ring resonators is demonstrated, proving the capability of a multi species monitoring when the rings are coated with different receptor molecules.

Gold nanorods have the potential to be employed as extremely bright molecular marker labels. However, samples containing a large number of gold nanorods usually exhibit relatively wide spectral lines. This linewidth limits the use of the nanorods since it would be rather difficult to image several types of nanorod markers simultaneously. We measured native scattering spectra of single gold nanorods with the CLASS microscope and found that single gold nanorods have a narrow spectrum as predicted by the theory. That suggests that nanorod-based molecular markers with controlled narrow aspect ratios should provide spectral lines sufficiently narrow for effective biomedical imaging.

Isolated isolectronic traps in semiconductors are promising candidates for single-photon emitters because sharp emission lines with well-defined wavelengths are readily obtained. In this work, we study the emission from individual isoelectronic traps formed by nitrogen-nitrogen pairs in nitrogen delta (δ)-doped GaAs grown on (001) and (111)A substrates. We have found there is a remarkable difference in the polarization properties of luminescence for between (001) and (111) substrates, and successfully obtained unpolarized single photons by utilizing (111) substrate, which are desirable for the application to quantum cryptography. Unpolarized photons could also be obtained from nitrogen δ- doped GaAs/AlGaAs heterostructures grown on (001) substrates.

We have grown GaAs quantum dots (QDs) in Al_0.3Ga_0.7As matrix by droplet epitaxy for application in single photon sources. This growth method enables the formation of QDs without strain, with emission wavelengths of around 700 nm within the optimal detection range of cost effective silicon detector, and with reduced surface density of several tens to a few QDs per μm² for easier isolation of single QDs. The optical properties of QDs were envisaged by exciton and biexciton emission peaks identified from power dependent and time-resolved micro-photoluminescence (μ-PL) measurements. The possibility of fabricating photonic crystal (PC) resonator including a single QD was shown by obtaining precise spectral and spatial information from a few QDs in a mesa structure, utilizing cathodoluminescence (CL) measurements.

We demonstrate the fabrication of highly efficient sources of entangled photon pairs by inserting a semiconductor quantum dot in an optical cavity. Two electron-hole pairs trapped in a quantum dot (QD) radiatively recombine emitting a cascade of two polarization entangled photons. To extract both photons, we use a photonic molecule consisting of two identical micropillars, one empty, the other embedding a chosen QD. By adjusting the diameter of the pillars and their relative distance, we ensure that both optical transitions of the QD are simultaneously resonant to cavity modes. The emitted photon pairs are efficiently extracted thanks to Purcell effect. Doing so, we obtain the brightest sources of entangled photon pairs to date. We further show that the implementation of Purcell effect allows increasing the fidelity of the two photon state by reducing spin induced phase shift during the radiative cascade.

In the last few years considerable effort has been devoted to the miniaturization of quantum information technology on semiconductor chips; in addition, recent developments in quantum information theory have roused a growing interest in 'generalized' states of frequency correlation. Parametric generation in semiconductor waveguides allows roomtemperature operation in the telecom range. We propose and compare some microcavity-based schemes for the generation of counterpropagating photon pairs and we experimentally demonstrate a bright source emitting 1.2 × 10^-11pairs/pump photon for a 1.8 mm long waveguide. The indistiguishability of the photons of the pair is measured via a Hong-Ou-Mandel two-photon interference experiment showing a visibility of 85 %. The versatility of the source to control the generated two-photon state is also discussed.

We report an ultra-low-noise single-photon detection at 1550nm using a 1-GHz sinusoidally gated InGaAs/InP avalanche photodiode. The avalanche photodiode was operated in a low temperature regime ( > 183 K) which can be achieved by a simple electrical cooling system. At 183 K, the dark count probability can be reduced to 2.0×10^-7 with a detection efficiency of 9.6 %, while the afterpulsing probability remained at a low value (3 %).

InGaAs/InP Single-Photon Avalanche Diodes (SPADs) have good enough performance to be successfully employed in many applications that demand to detect single photons in the 1 - 1.7 μm wavelength range. However, in order to fully exploit such InGaAs/InP SPADs, it is mandatory to operate them in optimized working conditions by means of dedicated electronics. We present the design and experimental characterization of a high-performance compact detection module able to operate at best InGaAs/InP SPADs. The module contains a pulse generator for gating the detector, a front-end circuit for avalanche sensing, a fast circuitry for detector quenching and resetting, a counting electronics, and some subcircuits for signal conditioning. Experimental measurements prove the state-of-the-art performance and its great flexibility to adapt it to the different applications.

Single-photon detectors play an increasing role in emerging application areas in quantum communication and low-light level depth imaging. The single-photon detector characteristics have a telling impact in system performance, and this presentation will examine the role of single-photon detectors in these important application areas. We will discuss the experimental system performance of GHz-clocked quantum key distribution systems focusing on issues of quantum bit error rate, net bit rate and transmission distance with different detector structures, concentrating on single-photon avalanche diode detectors, but also examining superconducting nanowire-based structures. The quantum key distribution system is designed to be environmentally robust and an examination of long-term system operation will be presented. The role of detector performance in photon-counting time-of-flight three-dimensional imaging will also be discussed. We will describe an existing experimental test bed system designed for kilometer ranging, and recent experimental results from field trials. The presentation will investigate the key trade-offs in data acquisition time, optical power levels and maximum range. In both examples, experimental demonstrations will be presented to explore future perspectives and design goals.

We discuss high-speed electronics that support the use of single-photon avalanche diodes (SPADs) in gigahertz singlephoton communications systems. For InGaAs/InP SPADs, recent work has demonstrated reduced afterpulsing and count rates approaching 500 MHz can be achieved with gigahertz periodic-gating techniques designed to minimize the total avalanche charge to less than 100 fC. We investigate afterpulsing in this regime and establish a connection to observations using more conventional techniques. For Si SPADs, we report the benefits of improved timing electronics that enhance the temporal resolution of Si SPADs used in a free-space quantum key distribution (QKD) system operating in the GHz regime. We establish that the effects of count-rate fluctuations induced by daytime turbulent scintillation are significantly reduced, benefitting the performance of the QKD system.

In order to acquire low-level optical signals with picosecond resolution, Single-Photon Avalanche Diodes (SPADs) are exploited thanks to their extreme performance. For many demanding applications, there is a growing need to operate such detectors with advanced instrumentation, specifically designed for efficiently exploiting the best performance in terms of sensitivity, timing resolution, fast-gating capabilities, etc. To this purpose we designed, tested and employed an ultra-fast pulse generator, a fast gated-counter and a wide-band delayer. The pulse generator is designed for gating SPADs with fast transition times (less than 100 ps), when it is needed to avoid unwanted photons that either precede or follow the useful signal. The gated counter acquires photons in well-defined time windows, programmable from 100 ps up to 10 ns. Finally, a wide-band delayer provides programmable delays, ranging from 25 ps up to 6.4 ns in steps of 25 ps. Such a delayer can be used to synchronize signals in many different experimental setups.

Remarkable advances in semiconductor technology as long as improvements in device design resulted in today's Silicon Single Photon Avalanche Diodes (SPADs) that are widely used in many demanding applications thanks to their excellent performance. However a lot of work is still be done in order to simultaneously meet three requirements crucial in a large number of applications, i.e. high Photon Detection Efficiency (PDE), good timing resolution and suitability for the fabrication of arrays. We will report on our advances on the development of a new planar silicon SPAD with high photon detection efficiency (PDE) and good photon timing resolution. A thick epitaxial layer allows for the absorption of a significant fraction of photons even at the longer wavelengths, while a suitable electric field profile limits the breakdown voltage value and the timing jitter; biased guard rings are also included to prevent edge breakdown. Preliminary results show that the new devices can attain a PDE as high as 30% at a wavelength of 800nm while keeping photon detection jitter below 100ps.

Due to their unique technical properties, the importance of semiconductor nanocrystal quantum dots (QDs) increased over the last decades especially for the use of quantum dot light-emitting diodes (QD-LED) [1,2] or detectors [3]. In present QD-LED arrangements, layer stacks e.g. hole injection layer (HIL), hole transport layer (HTL), QD layer (QDL), hole blocking layer (HBL), and electron transport layer (ETL) are mostly formed by two or more process steps including spin-coating, thermal deposition or vapor deposition. The latter in general is used for assembling the ETL, because the QDs active matrix group (ligands) is unstable for organic solvents. Nevertheless a reduction of process steps and thus decreasing material consumption could be an advance in manufacturing QD-LEDs. Therefore we discuss the fabrication of an all-spin-coated CdSe/ZnS core shell type QD-LED only consisting of HIL, QDL, and ETL showing electroluminescence at 610 nm. Thereby the used ETL additionally fulfils the function as HBL. Although the ETL has high electron mobility, the QD-LEDs conductivity was improved further through thermal annealing steps while fabrication.