In order to adapt to the third generation of infrared focal plane readout circuit design, this paper designs a 640x512-5μm InGaAs short-wave infrared focal plane readout circuit design based on 0.18μm standard technology. Based on the analysis of each module, the design focuses on the pixel unit and the readout mode of the array. Noise reduction and gain amplification are realized by pseudo correlation double sampling technology. Finally, the design of four - channel output simulation circuit. According to the simulation results, the readout rate is 10MHz, the system default working frame frequency is 54Hz, the output swing is 1.7V, and the linearity is more than 99.9%.
III-V compound semiconductors have abundant features for various electronic, optoelectronic and photonic applications, all arise from variform magic combination of group III and group V elements formed binaries, resulting in ever-changing characteristics. In this paper, diversified ternaries, quaternaries and quinaries are presented geometrically based on the binaries of arsenide, phosphide and antimonide, mainly concerned of their bandgap, lattice constant and the lattice match domain on different substrates. The features of nitride and dilute nitride, bismide and dilute bismuth, as well as boride, are also discussed briefly. An overall observation of whole III-Vs may contribute to the comprehensive understanding of their latent capacity and sustainable development, along with many challenges.
Based on collection effect of photogenerated carrier, the front-illuminated planar type InGaAs short-wave infrared (SWIR) detectors were fabricated by using N-InP/i-In0.53Ga0.47As/N-InP double-hetero structure materials. The series of detectors with the same dimension of 200μm×200μm contain several lateral collection regions and the width of each collection region is 15μm. The photoelectric characteristics of the photoresponse, I-V, spectral response and detectability of detectors with the lateral collection structure and normal structure were further analyzed. The build-in electrical field could effectively collect the electron/hole pairs generated in the lateral collection regions, so the photoresponse of lateral collection detector at 296 K is quite uniform by the laser beam induced current (LBIC) technology. Furthermore, the average peak detectivity and the density of dark current of the detectors with lateral collection structure reached 2.90× 1012 cm·Hz1/2/W and 3.94 nA/cm2 at -0.1 V respectively. It turns out that the lateral collection structure could effectively improve the dark current properties compared with the normal structure.
In order to improve the detection sensitivity of single-photon detection infrared imaging camera image sensor, the study is based on the structure of InGaAs infrared focal plane detector array. By using ZEMAX software, the size and position changes of the imaging light spot of the micro-lens array in the case of incident at different field of view angles are compared and analyzed, and the structural parameters are optimized. A 64×64 Si refracted micro-lens array is designed and manufactured. The study established a microoptical measuring system for micro-lens arrays, including light source, optical fiber, collimation, imaging and measuring devices. The measuring method and process of the parameters are introduced briefly. The morphology, geometric structure parameters and focal length of the micro-lens can be measured, therefore, the micro-lens can be evaluated effectively. The results show that the micro-lens array has good surface profile, good geometric uniformity and good optical properties.
The infrared astronomy is a very important branch of astronomy. Imaging observation is the basic approach to conduct infrared astronomy observation. Therefore, infrared Focus Plane Array (FPA) detector is needed for an infrared telescope. Detection toward celestial body need the detector to have high performance like extremely low dark current and low readout noise. Therefore, we designed a test equipment based on a 640 × 512 InGaAs array detector with a cryocooler which can cool the detector down to 77K. The detector is InGaAs of SITP-Hu-I type which is sensitive to 0.9us ~ 1.7um band. The test equipment is composed of a vacuum cryocooling system, a mechanical system and an electronical system. The vacuum cryocooling system can provide a low-temperature vacuum environment for the detector, and the mechanical system provides firm supporting. The electronic system provides the driver and readout of the detector.
Highly uniform ball-shaped indium bump arrays with small pixel pitches down to 10 μm have been fabricated. Multilayer stacked metal contact electrodes covered by a thin SiNx dielectric layer serve as the under bump metallization. Indium bumps were thermally evaporated inside the SiNx openings on top of the electrodes. Wet lift-off of the indium bumps was achieved by using a negative photoresist with precisely controlled undercuts. By comparison to a recipe without the SiNx, the non-uniform reflow effect of the indium materials was effectively eliminated after the thermal treatment. A mean indium ball diameter of 6.05 μm with a small coefficient of variation of 2.6% was finally realized for 10 μm pitch arrays. These results demonstrate the fabrication method is promising to ensure a reliable flip-chip hybridization of ultra-fine pitch focal plane arrays to silicon readout circuits with high yield.
Inert gas packaging and vacuum packaging are the main packaging method of photodetectors. A multi-stage thermoelectric cooler (TEC) is used to provide low temperature environment for extended wavelength InGaAs focal plane. A gas charging device is established to study nitrogen and krypton gas packaging. The performance of multi-stage TEC under different packaging atmospheres is tested, and the temperature field distribution is simulated by finite element analysis using FLoEFD software. The results show that in inflatable environment the cold side of TEC can achieve low temperature below 220K for the extended wavelength InGaAs detector. Gas conduction heat loss and gas convection heat loss are introduced into the inflatable packaging compared with vacuum packaging, and the relationship between temperature difference and input current under different packaging atmosphere is obtained. The cooling effect of TEC in krypton gas packaging is superior to that in nitrogen packaging, and the temperature of the cold platform can reach 211K and 215K respectively under the same input current of 4.5A. The results of FLOEFD finite element analysis are basically in agreement with the measured results, and the temperature uniformity of the focal plane is good. Because of without using the getter, Inert gas packaging is an economical packaging method for infrared detector.
This article presents the fabrication of the front-illuminated planar type InGaAs infrared detector based on the lateral collection structure. The detector with the cutoff wavelength 1.7μm was fabricated on the NIN-type InP/InGaAs/InP hetero-structure materials with sealed-ampoule method using Zn3P4 as the diffusion source. And the detector with the dimension of 460μm×1000μm consists of four lateral collection regions and the width of each region is 15μm. Furthermore, the electrical properties and photo response characteristics were investigated between detectors with the lateral collection structure and normal structure. The Laser beam induced current (LBIC) map shows that the photoresponse of lateral collection InGaAs detector at 296 K is quite uniform and the photoresponse signals generated in the lateral collection regions are the same as them in PN junction regions. The lateral collection regions disappear from view since the electron/hole pairs generated in the regions are all collected by the electrical field of depletion region. It turns out that the average peak detectivity and the density of dark current of the detectors with lateral collection structure and normal structure is 3.22×1012 cm·Hz1/2/W and 3.00×1012 cm·Hz1/2/W, 4.85 nA/cm2 and 22 nA/cm2 at -100 mV respectively. Therefore, the lateral collection structure could substantially reduce the dark current by 70% compared with the normal structure.
This work is aimed at designing an optical nano-antenna structure to enhance the optical absorption in 1.0−1.7 μm and improve the performance of InP-based InGaAs sensors. We report comprehensive analysis of an optical nano-antenna structure of metallic ball array for surface plasmon enhancement of near-infrared photodetection. The enhancement capability of metallic ball array on InP substrate with periodicity in the range of 600−1200 nm and diameters in the range 100−300nm has been studied by theoretical modeling with a finite-difference time-domain(FDTD) method. Our simulation results show that the highest transmission efficiency is achieved when the diameter of the ball is around and the optimized periodicity of the ball array is around 800nm. After comparing the transmission spectra of the arrays made of different metals, silver is found to be the best. Because of the speciality of SPP modes, the enhancement relative to wavelengths near 1.1μm is obviously weaker than that near longer wavelengths. Coating a SiO2 film about 500nm over the arrays is found to be an effective solution to achieve higher transmission efficiency around 1.1μm.
In order to study the effect of different passivation films on the detector performance, the front-illuminated planar-type 256×1 element InGaAs/InP detectors were fabricated with SiNx film and SiO2 film. The SiNx film was deposited by plasma enhanced chemical vapor deposition (PECVD) and SiO2 film was deposited by magnetron sputtering technology. The electrical properties and photoresponse characteristics were investigated after the detector mounted on dewar. The photoresponse maps from laser beam induced current (LBIC) method show that the isolation of adjacent elements of the detector with SiNx film is better than the detector with SiO2 film. Furthermore, at room temperature the average density of dark current and the average peak detectivity of the two kinds of detector is 26.8 nA/cm2 and 41.2 nA/cm2 at 100 mV reverse bias, 1.21×1012 cm·Hz1/2/W and 1.08×1012 cm·Hz1/2/W respectively. Therefore, the detector with SiNx film deposited by PECVD could availably passivate the surface in comparison with the detector with SiO2 film by magnetron sputtering technology.
The extended InGaAs short wavelength infrared (SWIR) detector covers 1.0-2.5 μm wavelength, which plays an important role in weather forecast, resource observation, low light level systems, and astronomical observation and so on. In order to fabricate the high performance extended InGaAs detector, materials structure and parameters were characterized with Scanning Capacitance Microscopy (SCM), Scanning Spreading Resistance Microscopy (SSRM), the spreading of minority carriers and lattice quality were obtained. Mesa etching process, etching damage restoration technique and low temperature passivation technique were used in the fabrication of the extended InGaAs detector. The improvement of material structure and device process was studied by fabricating and measuring different perimeter-to-area (P/A) photodiodes and singledevice, respectively. The dark current density of the extended InGaAs detector obviously was reduced, about 2 nA/cm2 at 170 K. The 512×256 FPAs were fabricated, the peak detectivity and the quantum efficiency of which are 5×1011 cmHz1/2/W and 80%, respectively. The staring image yielded of the 512×256 FPAs is shown, which demonstrates very good imaging quality.
The spectral irradiance of moonlight and air glow is mainly in the wavelength region from visible to short-wave infrared (SWIR) band. The imaging over the wavelength range of visible to SWIR is of great significance for applications such as civil safety, night vision, and agricultural sorting. In this paper, 640×512 visible-SWIR InGaAs focal plane arrays (FPAs) were studied for night vision and SWIR imaging. A special epitaxial wafer structure with etch-stop layer was designed and developed. Planar-type 640×512 InGaAs detector arrays were fabricated. The photosensitive arrays were bonded with readout circuit through Indium bumps by flip-chip process. Then, the InP substrate was removed by mechanical thinning and chemical wet etching. The visible irradiance can reach InGaAs absorption layer and then to be detected. As a result, the detection spectrum of the InGaAs FPAs has been extended toward visible spectrum from 0.5μm to 1.7μm. The quantum efficiency is approximately 15% at 0.5μm, 30% at 0.7μm, 50% at 0.8μm, 90% at 1.55μm. The average peak detectivity is higher than 2×1012 cm·Hz1/2/W at room temperature with an integrated time of 10 ms. The Visible-SWIR InGaAs FPAs were applied to an imaging system for SWIR and visible light imaging.
The short-wavelength infrared (SWIR) InGaAs focal plane array (FPA) detector consists of infrared detector chip, readout integrated circuit (ROIC), and flip-chip bonding interconnection by Indium bump. In order to satisfy space application requirements for failure rates or Mean Time to Failure (MTTF), which can only be demonstrated with the large number of detectors manufactured, the single pixel in InGaAs FPAs was chosen as the research object in this paper. The constant-stress accelerated life tests were carried out at 70°C,80°C,90°C and100°C. The failed pixels increased gradually during more than 14000 hours at each elevated temperatures. From the random failure data the activation energy was estimated to be 0.46eV, and the average lifetime of a single pixel in InGaAs FPAs was estimated to be longer than 1E+7h at the practical operating temperature (5°C).
Reflow soldering is the primary method for Flip-chip bonding without high bonding pressure. Reflow process during
flip-chip technology in short wavelength infrared (SWIR) InGaAs/InP Focal Plane array (FPA) with indium solder was
studied in this paper. In order to analyze the formation of Indium oxide and its effects on Indium bump reflow process.
Indium bumps were investigated by X-ray Photoelectron Spectroscopy (XPS). The profiles of Indium bumps after reflow
were observed by scanning electron microscopy (SEM). The interaction between Indium and the metal in under bump
metallization (UBM) during reflow process was discussed. The current–voltage (I–V) curves of InGaAs/InP photodiodes
were measured before and after the reflow process. The dark current density at 0.1 V reverse bias of InGaAs/InP
photodiodes were studied. It was confirmed that the characteristics of InGaAs photodetectors haven’t degenerated after
reflow in this paper.
KEYWORDS: Indium gallium arsenide, Photodiodes, Modulation transfer functions, Sensors, Staring arrays, Diffusion, Near infrared, Absorption, Back illuminated sensors, Signal detection
Crosstalk characteristics of high density FPA detectors attract widespread attention in the application of electro-optical
systems. Crosstalk characteristics of near-infrared (NIR) InGaAs photodiodes and focal plane arrays (FPAs) were
studied in this paper. The mesa type detector was investigated by using laser beam induced current technique (LBIC) to
measure the absorption outside the designed photosensitive area, and the results show that the excess absorption enlarges
the crosstalk of the adjacent pixels. The structure optimization using the effective absorption layer between the pixels
can effectively reduce the crosstalk to 2.5%. The major crosstalk components of the optimization photodiode come from
the electronic signal caused by carrier lateral diffusion. For the planar type detectors, test structures were used to
compare the crosstalk of different structures, and the guard ring structure shows good suppression of the crosstalk. Then
the back-illuminated 32x32 InGaAs photodiodes with 30μm pitch were designed, and LBIC was used to measure its
lateral diffusion of the effective carriers and fill factor of photosensitive area. The results indicate that the fill factor of
detectors can reach up to 98% when the diffusion region is optimized, and the minimum response exists between two
neighborhood pixels. Based on these crosstalk measurement results and optimizing structure designs, the linear InGaAs
photodiodes were designed and thus the InGaAs FPA assembly was fabricated. The assembly shows higher
electro-optical performance and good improvement on crosstalk. The assembly was applied in infrared imaging system
and modulation transfer function (MTF) of FPA assembly was calculated to be above 0.50. The clear image based on
FPA assembly was obtained.
In this paper, we focus on the influence of thermal treatment on the passivation of silicon nitride (SiNx) film of p-i-n InGaAs detector. In our experiment, the perimeter/area (P/A) test diodes are fabricated by using two different device processes, and the relationship between the dark current density and P/A is investigated. The results indicate that the thermal treatment in the vacuum can be able to improve the passivation SiNx film effect and thus suppress the perimeterrelated current with the decrease of two orders of magnitude. Then the analysis of dark current source is carried out. The result shows that the sample with SiNx film through thermal treatment is composed of diffusion current and ohmic current, on the contrary, the other mainly consists of surface leakage current and diffusion current. It is illustrated that the passivation effect of SiNx was strengthened after thermal treatment and surface leakage current can be suppressed.
In this paper, the two-dimensional (2-D) simulations of p-i-n type InP/In0.53Ga0.47As/InP photodetector at low bias are presented. The modeling results fit the experimental results well, verifying the validity of our model and the desirability of the simulated results. In order to further optimize the detector structure, the effects of thickness and doping concentration of the absorption layer on the dark current are both simulated and discussed, the results can be explained by the depletion region width in the junction area, and the details are shown in the energy band diagrams and the electric field maps of the p-i-n InP/In0.53Ga0.47As/InP photodetector.
InxGa1-xAs ternary compound is suitable for detection in the shortwave infrared (1-3μm) band. The alloy In0.53Ga0.47As is lattice-matched to InP substrate and has a wavelength response between 0.9μm to 1.7μm at room temperature. The increase of indium composition can extend the wavelength response to longer infrared wave. With the Indium content 0.83, the cutoff wavelength can be extended to 2.6μm. In this paper, we reported the performance of 64x64 pixels mesa-type back-illuminated extended wavelength InGaAs detector arrays. The mesa type detectors were fabricated by ICP etching, side-wall and surface passivation by ICPCVD (inductively coupled plasma chemical vapor deposition) based on the MBE-grown p-i-n In0.83Al0.17As/In0.83Ga0.17As/InxAl1-xAs/InP epitaxial materials. The I-V characteristics and electro-optical performances of these detectors at different temperatures were measured, and the properties such as dark current, response spectra, responsivity, detectivity were analyzed. The results indicate that the dark current of In0.83Ga0.17As photodiodes decreases with decreasing temperature, varying from 4×10-4A/cm2 at 290K to 1.7×10-8A/cm2 at 180K. The spectral response showed slightly blue shift while the detectors were cooling down, and the cut-off wavelength is 2.57μm at room temperature and 2.43μm at 200K, respectively. The dark current density is 115nA/cm2 at 200K and -10mV bias voltage. The peak detectivity is 6.08E11cmHz1/2W-1.
Experimental setup for evaluating four-stage thermoelectric cooler’s performance was designed. Effects of input power, heat dissipation condition and heat load on the temperature difference (ΔT) of four-stage thermoelectric coolers’ hot and cold faces were obtained experimentally. The result shows that, the ΔT increases as the input power increases. A linear relationship exists between input current and feedback voltage. In different cooling conditions, the ΔT of thermoelectric cooler (TEC) increases with the temperature of hot face. As the temperature increasing on hot face is 1K, the ΔT increasing of TEC can be about 0.5K. Meanwhile, the power consumption of TEC also increases slightly. Water condensation can be prevented in either dry nitrogen environment or vacuum environment, but the vacuum level has great influence to the ΔT, especially in low operation temperature. The better the vacuum level is, the smaller the convection heat loss has. When the operation temperature of focal plane array (FPA) is lower than 220K, it is prior to use vacuum packaging. Considering the Joule-heat of readout circuit and the heat loss of wire conduction, the minimum working temperature of FPA can reach below 200 K when the temperature of the hot face is 285K. And the coefficient of performance (COP) of TEC can increase sharply from 0.8% to 4% when the controlled operation temperature is 220K rather than 200K.
Extended wavelength InGaAs photodiodes in 1.0~2.5μm spectral rang based on two types of material structures were investigated systematically. The first type InGaAs photodiode, marked by sample 1#, was fabricated using MOCVD epitaxial materials with P-i-N structure. The second type InGaAs photodiodes, marked by sample 2#, was fabricated using MBE epitaxial materials with P-i-N structure. The two types of photodiodes were fabricated by mesa etching technique, side-wall and surface passivation film. Dark current and voltage curves were measured by semiconductor parameters analyzer at different temperature, and dark current characteristics were analyzed using different perimeter to area method. The mechanism of the devices has been analysed. Polarization microscopy and conductive atomic force microscopy (c-AFM) have been used to investigate the local conductivity of the photodiodes’ sensitive area. Combining the optical and c-AFM micrographs with dark current characteristics, we intended to characterize the relationships of the leak current and the defect. The results indicate that sample 1# has relative much more leak defects than that of sample 2#, and thus the dark current sample 1# is higher than that of sample 2# and. The defects are generated at the body of material and spread to the surface, and these defects cause very high dark current of sample 1#.
Back-illuminated near-infrared detectors were designed and fabricated using p-InGaAs/p-InP/i-InGaAs/n-InP p-i-n layer structure. In order to optimize the detector layer structure, the device was simulated by drift-diffusion simulator “SimWindows” first, and then the epitaxy material was grown by metal organic chemical vapor deposition (MOCVD). The current-voltage characteristics of the fabricated detectors with and without light were investigated respectively. The results show that the responsivity of the detectors is around 0.7 A/W, and the dark current is about 1×10-4 A/cm2 at reverse bias 0.1V, both of which are comparable to the simulated results. Our results also show the smaller detector has better dark current density, and the dominated mechanisms of dark current are discussed in the paper.
The In0.53Ga0.47As p-i-n detectors with different cap layer which are InP, In0.52Al0.48As without secondly doping,
In0.52Al0.48As with epitaxial growth of In0.53Ga0.47As layer and In0.52Al0.48As with secondly doping, respectively, were
fabricated. The photoelectric performances of the detectors have been investigated. The result indicated that In0.52Al0.48As
cap layer lead to a reduction of dark current compared to InP, but the bad contact property on In0.52Al0.48As can lead to a
reduction of quantum efficiency. To get a low resistance contact on p- In0.52Al0.48As, the two methods have been used
which are epitaxial growth of In0.53Ga0.47As layer and forming a heavily doped layer on p-InAlAs layer with secondly
doping. Although the two methods mentioned above were all beneficial for the contacts properties, epitaxial growth of
In0.53Ga0.47As layer can cause deterioration of the property of the detector. The result indicates that the In0.52Al0.48As with
secondly doping used as cap layer can lead to lower dark current (dark current density is 116nA/cm2 at -0.01V) and
larger quantum efficiency. The mechanism of dark current and the response spectrum for different samples have also
been investigated, for the sample with the In0.52Al0.48As cap layer with secondly doping diffusion current is the main
current mechanism.
InGaAs ternary compound is suitable for detector applications in the shortwave infrared (SWIR) band. Due to the advantages of good stability, low cooling requirements and high detectivity, InGaAs detectors have been applied widely in the space remote sensing area. However, InGaAs detectors would be affected by strong sunlight direct irradiation in space application. In this paper, a mesa-type InGaAs detector with large sensitive area of diameter 5mm was designed based on InP/In0.53Ga0.47As/InP epitaxial material, which is lattice-matched to InP substrate. The InGaAs detectors were fabricated by ICP etching, and packaged in a Kovar shell. The relative spectral response is in the range of 0.9μm to 1.7μm. The mechanism of the sunlight direct irradiation on InGaAs detector performance was studied. The sunlight were focalized by lens and irradiated directly on the detector. A piece of epitaxial material was investigated at the same time which was cleaved from a 2 inch wafer, same to the detector material. The real time testing was taken out to observe the output signal of the detector. After the irradiation experiment, the I-V curves and the relative response were tested immediately. The dark current of the detector increased temporarily, but come back to the original level after 24 hours. The response spectrum was nearly not affected. The XRD testing of the epitaxial material sample was carried out before and after sunlight direct irradiation. The sunlight irradiation causes thermal stress degradation. The thermal electrons were produced by the absorption of a great deal of visible light, leading to local enhancement of temperature and the lattice degeneration of the material.
It is well known that In0.53Ga0.47As epitaxial material is lattice-matched to InP substrate corresponding to the wavelength from 0.9μm to 1.7μm, which results to high quality material and good device characteristics at room temperature. In order to develop the near infrared multi-spectral imaging, 512×128 pixels InGaAs Near Infrared Focal Plane Arrays (FPAs) were studied. The n-InP/i-InGaAs/n-InP double hereto-structure epitaxial material was grown by MBE. The 512×128 back-illuminated planar InGaAs detector arrays were fabricated, including the improvement of passivation film, by grooving the diffusion masking layer, the P type electrode layer, In bump condition and so on. The photo-sensitive region has the diffusion area of 23×23μm2 and pixel pitch of 30×30μm2 . The 512×128 detector arrays were individually hybridized on readout integrated circuit(ROIC) by Indium bump based on flip-chip process to make focal plane arrays (FPAs). The ROIC is based on a capacitive trans-impedance amplifier with correlated double sampling and integrated while readout (IWR) mode with high readout velocity of every pixel resulting in low readout noise and high frame frequency. The average peak detectivity and the response non-uniformity of the FPAs are 1.63×1012 cmHz1/2/W and 5.9%, respectively. The power dissipation and frame frequency of the FPAs are about 180mW and 400Hz, respectively.
Nanowire grating is designed within the wavelength range from 1μm to 3μm according to the sensitive wavelength of InGaAs short wave infrared (SWIR) detector. The polarization performance is analyzed on the basis of finite difference time domain (FDTD) method. In order to improve the polarization performance, we insert a SiO2 dielectric grating between metal grating and substrate to form Au-SiO2 hybrid grating. The numerical study shows transmittance of hybrid grating is almost 88%which is 18% higher than monolayer metal grating at 1.8μm. In addition, the hybrid grating with the grooved- SiO2 layer has higher transmittance efficiency than those with smooth SiO2 layer for special wave band. By optimizing the specific parameters of the hybrid grating such as period, thickness and the groove depth of SiO2, finally we obtain the optimal parameters of the designed hybrid grating: the grating period is 0.4 μm, the thickness and groove depth of SiO2 are 0.4μm and 0.1μm respectively. Numerical study shows that the designed grating has advantages of wide band, high transmittance efficiency and high extinction ratio.
The single-pixel extended wavelength mesa InGaAs/InAsP SWIR detector was reported. The properties of the detector were characterized and analyzed at 160K~300K. At the operating temperature of 200K , the dark current density is 1.37×104 nA/cm2(@-10mV), the cut-off wavelength is 2.43μm, the peak detectivity and the peak responsivity are 3.44×1011cmHz1/2W-1 and 1.41A/W, respectively. Through analysis of the dark current source, the analysis of reverse dark current indicates that the tunneling current plays an important role at high voltage or relatively low temperature, and at near room temperature and low bias voltage, the generation-recombination current is the main current source instead of ohmic current based on thermal activation energy approximate to Eg/2 and the bias-voltage characteristic of the first order derivative of dark current, while the zero-voltage current mainly consists of the interface current and the thermal background current.
Extended wavelength InGaAs infrared detector arrays in 1.0~2.5μm spectral rang based on three types of material structures grown by MBE were studied. The first type InGaAs detectors, marked by sample 1#, were fabricated using Pi- N epitaxial materials, mesa etching technique, side-wall and surface passivating film. The second type InGaAs detectors, marked by sample 2#, were fabricated using N-i-P epitaxial materials, mesa etching technique, side-wall and surface passivating film. The third type InGaAs detectors, marked by sample 3#, were fabricated using n-i-n epitaxial materials, planar diffusion process and surface passivating coating. I-V curves, low frequency noise and response spectra of these detectors were measured at the different temperature. The response spectra of these detectors cover 1.0~2.5μm wavelength range. The dark current density of three types InGaAs detectors are 28nA/cm2, 2μA/cm2, 9μA/cm2 at 200K and -10mV bias voltage, respectively. Compared to Sample 2# and Sample 3#, sample 1# presents the lower dark current at the same temperature and the same bias voltage, which mainly results in the improvement of surface passivation film and the depth of mesa etching. The frequency spectrum of the noise of sample 1# has an inflection point at about 10Hz frequency, 1/f noise play an obviously role in the detectors below the 10Hz frequency.
A planar-type InGaAs linear detector was designed and fabricated based on n-i-n+ type InP/In0.53Ga0.47As/InP epitaxial
materials. The major process of the detector contains planar diffusion, surface passivation, metal contact and annealing.
The I-V curves and the relative spectral response were measured at room temperature. The relative spectral response is in
the range of 0.9 μm to 1.68 μm. The R0A of the detector is about 2×106 Ω•cm2 and the dark current density is
5~10nA/cm2 at -10mV bias voltage. The linear detectors were wire-bonded with readout integrated circuits (ROIC) to
form focal plane array (FPA). The input stage of the ROIC is based on capacitive-feedback transimpedance amplifier
(CTIA) with a capacitor (Cint) to be 0.1pF. However, the FPA signals are oscillating especially when close to the
saturation. The ohmic contact on p-InP region plays an important role in the performance of detectors and FPAs. In this
case, the series resistance to p-InP layer of each pixel is up to 1×106Ω. The FPAs were simulated in case of InGaAs
detectors with different series resistances. According to the simulation results, the bandwidth of CTIA is lowering along
with Rs increasing, and the signals of the FPAs oscillate when the series resistances are beyond 4×104Ω. The reason for
the unstable oscillation of FPA is due to the series resistance of the detector which is too high enough. Then, the
annealing process of the detectors was improved and the series resistances were lower than 1×104Ω. The optimized
InGaAs linear detectors were wire-bonded with the same ROIC. The oscillation of the signals disappears and the FPA
shows good stability.
InxGa1-xAs ternary compound is suitable for detector applications in the shortwave infrared (1-3 μm) band. In this paper,
we reported on mesa type and planar type extended wavelength InGaAs detector arrays. The photo response
performances of these detector arrays were investigated. The blackbody responsivities (Rbb) of these detectors at different
temperatures were measured, and the results showed that the Rbb of planar type arrays was higher than that of the
conventionally passivated mesa type, but the mesa arrays fabricated by improved passivating technique has the highest
responsivity. The reason of the Rbb difference between the arrays was analyzed, and it is found that the difference mostly
comes from the minority carrier lifetime, which is related to the device structures and fabrication processes. With the
optimized fabrication processes the mesa type arrays can obtain higher blackbody responsivity even more than the planar
arrays.
According to excellent photoelectric properties of InGaAs epitaxial material, and important application of the spectral
bands at center wavelength of 1.38 μm and 1.60μm, the new-type monolithic dual-band InGaAs detector is studied in
this paper. The detector was designed and fabricated with mesa structure and Fabry-Perot cavity by thermal evaporation.
The current-voltage characteristics, response spectra of monolithic detector were measured. The bandwidths of 1.38 μm
and 1.60μm waveband detector are 46nm and 54 nm respectively. A 400×2 dual-waveband monolithic detector was
wire-bonded with two 400×1 readout circuits, to form 400×2 dual-waveband InGaAs focal plane arrays (FPAs). At room
temperature, the detectivity D*, non-uniformity, response bandwidth and the non-operative pixel ratio of 1.38 μm
waveband FPAs are 7.71×1011cmHz1/2/W, 6.20%, 46nm and 0.25%, respectively, and the ones of 1.60 μm waveband FPAs are 6.06×1011cmHz1/2/W, 3.20%, 54nm and 0.25%, respectively. The monolithic dual-waveband InGaAs focal plane arrays (FPAs) plays an important roles in developing compact, low-cost and high-precision photoelectric detection (imaging) system.
The short wavelength infrared (SWIR) band near 1.0-3.0μm plays an important role in many applications such as weather forecast, earth environmental or resource observation, low light level systems and astronomical observation. It is well known that InGaAs detectors can shift the cutoff wavelength from 1.7μm to 2.5μm with the higher fraction of indium in the ternary InXGa1-XAs material grown on InP, which results to material defects and poorer device characteristics due to the lattice mismatch. Dark current characteristics of extended wavelength InGaAs detectors were investigated in this paper. Dark current mechanisms for extended InGaAs detectors with different absorption layer parameters and device fabrication process were analyzed according to current-voltage curves at different temperatures and bias voltages. Activation energy of devices was extracted from current-voltage curves. Activation energy is related with absorption layer concentration and test temperature. Activation energy is the higher for the devices with the higher absorption layer concentration at lower bias voltage at the same temperature range, which shows that the narrower width of the depletion layer in the devices results to the lower generation-recombination current. The devices with the optimized etching and passivation parameters show higher thermal activation energy and the lower dark current. Dark current mechanisms of the ones are dominated by diffusion current at the higher temperature and lower bias voltage, whereas dominated by internal generation-recombination current and ohmic leakage current at the lower temperature.
The laser-induced damage threshold (LIDT) of optical thin film is influenced by certain preconditioning processes.
HfO2/SiO2 532nm high reflective multi-layers were prepared by electron beam evaporation and were preconditioned by
532nm laser. The 532nm LIDT, surface condition, and damage morphology of the sample were characterized and
compared before and after laser conditioning process. Results are presented that the LIDT of e-beam deposited
multilayer HfO2/SiO2 thin films can be increased after laser conditioning. Possible reasons for such enhancement have been analyzed.
For realizing miniature and integration of the near infrared (NIR) detector and satisfying the requirement of the miniature
and integration of the photoelectric detection system, the filter films centered on 1.38 μm were fabricated by using
thermal evaporation and alternating Si/SiO2 layers upon InP substrates. The filter film contains a three-cavity fabry-perot
structure, the peak of transmission is about 60%, and its full width at half-maximum ranges from 20 to 50 nm. To
investigate the temperature stability of the filters, several samples were annealed at different temperature above 250 ℃.
The surface morphology of the filter films before and after annealing was characterized by polarized light microscope,
and temperature stability of the center wavelengths is examined in the 1380-nm wavelength region by Fourier Transform
Infrared Spectroscopy (FTIR). It indicates that there are several points of film falling off because of micro-defect. After
annealing, the peak value of the transmission decreases, and the center wavelengths have a blue shift ranging from 20 to
40 nm and the bandwith has an increase of around 8 nm.
This article presents the fabrication of the front-illuminated planar type InGaAs sub-pixels infrared detector with the cutoff wavelength 1.68µm based on the lateral collection effect of photogenerated carriers. The detector with the dimension of 385µm×500µm consists of five sub-pixels and each of which has two sub-elements. The electrical properties and photo response characteristics were investigated after the detector mounted on Dewar. The photoresponse map from Laser beam induced current (LBIC) method shows that the detector has good photoresponse uniformity at 296K which indicates the electron/hole pairs generated in the lateral collection regions are all collected by the nearest sub-elements. The minority carrier diffusion length Lp is about 19.6µm at 296K. The density of dark current is 13.4nA/cm2 at 100mV reverse bias and the peak detectivity is 3.4×1012cmHz1/2W-1 at room temperature. By reducing the diffusion region, the detector could effectively decrease the lattice damage and corrosion spots in the cap layer caused in the PN junction formation without sacrificing detector performance. Therefore, this structure could availably reduce the ratio of dead pixels, suppress the extension of photo-sensitive area and the optical cross-talk in photo detector arrays.
InxGa1-xAs ternary compound is suitable for detector applications in the shortwave infrared (1-3 μm) band. The alloy In0.53Ga0.47As is lattice-matched to InP substrate, which leads to high quality epitaxial layers. Consistently the In0.53Ga0.47As detector shows low dark current density and high detectivity at room temperature with wavelength response between 0.9 and 1.7 μm. In this paper, planar-type 24×1 linear InGaAs detector arrays with guard-ring structure were designed and fabricated based on n-i-n+ type InP/In0.53Ga0.47As/InP epitaxial structure by sealed-ampoule diffusion method. At first the dark current density is about 30~60 nA/cm2 at -0.1 V at room temperature. After modifications to the detector design and processing, the dark current density reduces to 2~9 nA/cm2 at -0.1 V at 293 K. The ideality factors simulated from I-V curves come close to 1 and less than the factors of previous detectors, which indicates that the dark current is dominated by diffusion current, while the generation-recombination current exhibits in the previous detectors. At the temperature of 293 K, the R0A of the detector reaches more than 1×107 Ω·cm2, the relative spectral response is in
the range of 0.9 μm to 1.68 μm, the mean peak responsivity is 1.2 A/W and the mean peak detectivity is more than 3.0×1012 cm·Hz1/2/W.
A chemistry of halogen mixed with neural or inert gas is mostly used for ICP etching of III-V compound semiconductor.
The neural or inert gas has an effect of desorption and dilution, on the other hand, damages in the lattice due to ion
bombardment are induced, which result in difficulties in improving the performances of detectors. Good desorption and
passivation was obtained by using a new etching technology with the mixed gas of methane and hydrogen instead of
neural or inert gas, and the damages caused by physical bombardment were much less because of the small quality of
radical. The sample etched by using this technology was compared with the ones by using etching of neural or inert gas.
The influences of ICP etching process parameters on etch rate, surface roughness and surface damage were investigated
by using orthogonal experimental design. The methods of scanning electron microscopy (SEM) and X-ray Diffraction
(XRD) were used to investigate the surface profile and surface damage respectively. And according to the experimental
results, the process parameters are optimized. Finally, a feasible etching technology with low damage, good surface
profile and good controllability was achieved.
With the development of material growth and device technologies, the pixel density becomes much higher. The pixel size and the spacing between pixels have been becoming smaller and smaller, causing the cross talk of the neighboring pixels acuter. Linear InGaAs detector arrays with 25 μm pitch and 2 μm spacing were fabricated, and the modulation transfer function of detector arrays with infrared lens was measured using a system of collimator tube. A tiny light dot produced by the collimator tube was used to analyze and calculated the cross talk of the detector with conserved absorber around the photosensitive mesa, and the cross talk between two neighboring pixels was approximately estimated. With the conserved absorber structure, the electronic cross talk is dominant in the cross talks between neighboring pixels.
To improve the operability and rate of final products significantly, a novel process was proposed. Detectors with
cutoff wavelength at 1.7 μm and 2.4 μm were fabricated in different processes, and the electricity characteristics and
spectral response were measured. The novel process was analyzed by comparing the characteristics of the detectors. The
dark current and responsibility of the detectors with cutoff wavelength at 1.7 μm fabricated in the new process were
improved. However, the new process has negative effect on the detectors with cutoff wavelength at 2.4 μm. The pnjunction
degenerated and the leakage current increased sharply. In order to find the reasons of degeneration, the methods
of Auger electron spectroscopy (AES) and scanning capacitance microscope (SCM) were used. The results indicate that
the metal elements do not penetrate into the pn junction causing the sharp increase of leakage current, while the interface
states due to lattice mismatch are thermally activated causing the degeneration of pn- junction.
In this paper, dry etching of In0.8Al0.2As/In0.8Ga0.2As/In1-xAlxAs (In1-x-yAlxGayAs) epitaxy material was studied in
BCl3/Cl2/Ar inductively coupled plasma (ICP). Etching behavior was characterized by varying the BCl3/Cl2/Ar mixing
ratio, ICP power or DC-bias. The results indicate that, in Cl2 dominant condition, smooth surfaces are achieved with
mean etch rate exceeding 2 μm/min. As the ratio of BCl3 increasing, the etch rates decrease monotonously and the
surfaces becomes rougher because of low volatility InClx etch product. ICP power influences the etch rates, and the etch
rates increase monotonously with DC-bias. The result is useful for the fabrication of extended long-wavelength response
optoelectronic InGaAs devices.
Nowadays, GaN-based multi-layer materials is developing fast, and it is important to know their
interface and optical properties for devices design and fabrication. In this letter, the transmission
spectra are analyzed, and the dependence of the transmission spectra on parameters of the samples is
discussed. Sequentially, we obtain the transmission spectra of a series of GaN-based samples.
Simulation of the transmission spectra is done and useful information is extracted. For one of our
samples, the refractive index varies a little between 2.518 and 2.305 with the wavelength from 400 to
800nm, while the extinction coefficient is 6x-10-9.5exp(2700/λ), and the thickness is 2860nm. Finally,
we get the dispersion relationship of the GaN and AlGaN films, and it is compared with the results of
some other research groups.
In this work, an innovated Si3N4 as an out-diffusion barrier layer to Au/Zn/Au contact system for p-type InP has been
proposed. Before the contacts were annealed, Si3N4 layer was deposited on the Au(200Å)/Zn(700Å)/Au(200Å), then the
Si3N4 was removed by HF and a 2000A layer of pure gold was deposited to facilitate wire bonding. The specific contact
resistance dropped to a minimum value of 6×10-7 Ω • cm2 (for an acceptor concentration of about 3×1018cm-3) and the
contact became perfectly Ohmic. Besides, Si3N4 layer is an excellent passivation layer and antireflection coating in
InP/InGaAs/InP (p-i-n) photodiodes.
The uncooled InGaAs-based infrared detector has received great interest in recent years for its application in optical-fiber
communication and remote sensing. However, the improvement of device performance is hampered by the lack of
feasible method to monitor its device process. The Microwave Photoconductivity Decay (μ-PCD) technique is a
contactless and non-destructive technique of the recombination lifetime characterization and mapping and has found
wide application in semiconductor research. In this paper, a double heterojunction p-i-n InP/In0.53Ga0.47As/InP mesa
structure was fabricated by Ar+ ion etching and the μ-PCD technique was applied to characterize the electrical effects of
ion etching on this structure. The results revealed that the built-in field in the p-n junction played a critical role in
recombination of photo induced minority carriers which made the mesa structure identifiable but not identical with the
lifetime mapping of the sample. The recombination lifetime in the mesa was dominated by the recombination process in
the edge of the mesa. The lifetime in the etched region was also influenced by the built-in field and increased with the
decrease of distance to the mesa area. And ion etching brought great nonuniformity to the photo active cells.
256×1 element linear InGaAs detector arrays assembly have been fabricated for the short wave infrared band(0.9~1.7μm), including the detector, CMOS readout circuits, thermoelectric cooler in a sealed package. The InGaAs detectors were achieved by mesa structure on the p-InP/i-InGaAs/n-InP double hetero-structure epitaxial material. 256×1 element linear InGaAs detectors were wire-bonded to 128×1 element odd and even ROIC, which were packaged in a dual-in-line package by parallel sealing. The characteristics of detectors and detector arrays module were investigated at the room
temperature. The detector shows response peak at 1.62μm with 50% cutoff wavelength of 1.73μm and average R0A with 5.02KΩ•cm2. Response non-uniformity and average peak detectivity of 256×1 element linear InGaAs detector arrays are 3.10% and 1.38×1012cmHz1/2/W, respectively.
In this work, the performance of InxGa1-xAs photovoltaic detectors with cutoff wavelength of 2.4μm(x=0.78) were
investigated. The detector arrays were fabricated using gas source molecular beam epitaxy (GSMBE) grown material and
arranged in linear arrays of 256 pixels of 56×56μm2 dimension. The transition of the large lattice mismatch (1.6%)
between the substrate and the absorption layer was dealt with a linearity transformation InxGa1-xAs buffer layer. The
dark-current performance achieved is as low as 10-10A at 300K and a bias voltage of -0.5V. This corresponds to a figure
of merit for detector resistance R0 times detector pixel area A of R0A =3.5~7.5Ωcm2 at 300K and quantum efficiency
above 60%. Room temperature D*(λp) values beyond 3×1010cmHz1/2W-1.
A CMOS 512×1 readout integrated circuit (ROIC) for an IR
focal-plane-array (FPA) has been designed. The pixel pitch
is 25um. The input stage is the capacitance trans-resistance amplifier (CTIA) and a correlated double sampling (CDS)
circuit is included in each unit. In order to avoid the waste of the threshold voltage in the process of sampling, a matched
CMOS sample switch was used in CDS. The simulation results show that, if the output voltage of the preamplifier
decreases during the integration process, using pMOS source follower can achieve the maximal output swing. Since the
512 elements shared one output channel, the readout rate was limited due to the large capacitance at the output node. So
an off-chip changeable resistance was chosen as the load of the source follower to balance the gain and speed. The
timing diagram of the driving signals was presented and discussed. Finally, the simulation results are presented, using
Cadence spectreS. The saturated differential output swing is 2.1V at 1MHz pixel readout rate, under the condition of
2.5V reference voltage and a 10k Ω load.
In this paper, 256 elements front-illuminated InGaAs mesa detector arrays were fabricated based on doped-InGaAs
absorbing layer in MOCVD-grown p-InP/n-InGaAs/n-InP
double-heterostructure epitaxial materials. The processing
includes mesa-making, SiNx passivation, growth of electrodes and so on. The current-voltage, capacitance-voltage
characteristics and response spectrum of the detector were measured. The results indicate that the InGaAs detector has
typical dark current about 0.9 nA at 0.5 V reverse-bias voltage, a capacitance as low as 49 pF at 1 reverse-bias voltage,
and the peak wavelength and cutoff wavelength at 1.57μm and 1.68μm respectively. The InGaAs detector arrays were
connected with two CTIA-structured L128 read-out integrated circuits, and the response signal and noise were obtained.
At room temperature, the mean peak detectivity of the InGaAs focal plane arrays (FPAs) is 1.9×1012
cmHz1/2W-1, and the
non-uniformity of response is superior to 6%. The laser beam induced current (LBIC) technique was used to investigate
the crosstalk and photoactive area of the InGaAs detectors. Its results indicate that there is little crosstalk between two
neighbor InGaAs detectors, about 7%. The photoactive area of InGaAs detector extends about 4.5 μm, and the reason is analyed in the paper.
We found that the contact resistance of Au/Pt/Ti on p-InP increases with the increase of annealing time and annealing
temperature. Au/Pt/Ti is ohmic contact metal as deposited with specific contact resistance of 2.49×10-3 Ωcm2 when p-InP
doped by 7.5×1018 cm-3 and is Schottky contact when doped by 2×1018 cm-3. Surface morphologies of Au/Pt/Ti after rapid
thermal processing (RTP) were analyzed by atom force microscopy (AFM). An interface layer dominated by TiIn
compound, which increase the specific contact resistance, was found in Auger electron spectroscopy (AES) analysis.
P-InP and n-InP ohmic contacts can be achieved at the same time as deposited when added p-In0.53Ga0.47As layer on
p-InP/InGaAs/n-InP without annealing.
The contact of p-GaN was formed under different annealing condition, and its effect on p-i-n GaN-based
detectors was studied by current-voltage (I-V) measurements and the response spectra. The parameters of metal/p-GaN
interface were obtained by fitting the forward I-V curves. The results show that ideal factor of metal-semiconductor
( M-S) contacts annealed at 550°C for 3min is about 1.19, which means the formation of good ohmic contacts at the M-S
interface and leads a lower turn-on voltage. But metal/p-GaN contacts have no obvious effect on response spectra of
detectors.
In recent years, AlxGa1-xN semiconductor alloys, with a direct bandgap tunable between 3.4eV and 6.2eV, become the most suitable materials for the fabrication of UV detectors. In this paper we describe the fabrication and characteristics of an UV 64×1 focal plane array (FPA) based on front illuminated GaN p-i-n photodiodes. The diode structure consists of a base n-type layer of GaN followed by unintentionally doped and p-type layers deposited by metal organic chemical vapor deposition on GaN buffered sapphire substrate. Standard photolithographic, Ar+ ion beam etching, SiO2 passivation and metallization procedures were employed to fabricate the devices. I-V, responsivity and spectral response were tested. The linear photodiode array was indirectly hybridized to a silicon readout integrated circuit (ROIC) chip. The ROIC chip consists of capacitor feedback transimpedance amplifier (CTIA) input circuits, correlated double sampling (CDS) circuits, shift registers etc. The 64×1 UV linear FPA was packaged into a 28-pin chip carrier. The response ununiformity is 1.86%. The mean detectivity is about 2.0×109cmHz1/2W-1.
The contact resistivity of Ni/Au contact on p-type GaN was drastically decreased through the surface treatments in sequence using alcohol-based HCl and KOH solution. The surface oxide on p-type GaN formed during epitaxial growth was removed in the alcohol-based HCl and KOH solution, The O 1s and C 1s core-level peaks in the x-ray photoemission spectra showed that the alcohol-based HCl treatment was more effective in removing of the surface oxide layer. Compared to the KOH solution treated sample, the alcohol-based HCl-treated sample showed a Ga 2p core-level peak which was shifted toward the valence-band edge by 0.3 eV, indicating that the surface Fermi level was shifted toward the valence-band edge. These results suggest that the surface barrier height for hole injection from Ni/Au metal to p-type GaN be lowered by the surface treatment, which results in a drastic reduction in specific contact resistance.
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