The requirement for cooling below room temperature to limit thermal generation processes is the major drawback of infrared (IR) photon detectors. In order to obtain background limited performance (BLIP), the devices for the 3–5 μm spectral region are typically operating at T <200 K, while those for the 8–12 μm at 77 K. The current effort to produce near room temperature photon detectors (higher operating temperature conditions, HOT) are being concentrated on the interband cascade photodetectors (ICIP). That effort is mostly seen for longwave infrared (LWIR) devices operating at HOT conditions where the optimum absorber may be thicker compared to the carriers’ diffusion length, limiting the photogenerated carriers collection what leads to the decreasing of the quantum efficiency (QE) and the ultimate performance cannot be achieved in practice. The ICIP architecture allows to circumvent that issue. In addition to avoid the limitation imposed by the reduced diffusion length, the intersubband (IS) quantum cascade photodetectors (QCPs) were introduced in the early 2000s based on quantum-well infrared photodetectors (QWIPs) and quantum cascade lasers (QCLs). Those cascade detectors proved to be operating at low temperatures ~ 100 K. In this paper we present the current status of the ICIPs based on type-II superlattices (T2SLs) InAs/InAsSb n- and p-type doped active layers intended to be operating within LWIR range and HOT conditions - 210 K reached by thermoelectric coolers and room temperature. Immersed detector reached detectivity, D*~3×108 cmHz1/2/W at 300 K and wavelength, λ=10 μm.
Plasmonic enhancement has a great potential for performance improvement of high operating temperature (HOT) photodetectors, especially those optimized for long-wavelength infrared (LWIR). Conventional HOT photodetectors exhibit poor quantum efficiency (QE) due to short carrier diffusion lengths of narrow bandgap semiconductors and relatively low absorption coefficients within the LWIR range. Plasmon-driven subwavelength light confinement enables high absorption even in a very thin absorber that provides efficient carrier collection, boosting the detector QE. We propose a photovoltaic detector equipped with a two-dimensional subwavelength hole array (2DSHA) in gold metallization on InAs/InAsSb type-II superlattice (T2SL) heterostructure. Our numerical study utilizing the finite-difference time-domain (FDTD) method predicts five times increased absorption in comparison with a conventional, back-side illuminated device. The simulated behavior of the plasmonic structure was confirmed experimentally by transmittance measurements, which revealed resonant features corresponding to various plasmonic modes.
We report on LWIR multi-stage thermoelectrically cooled cascade photodiodes with InAs/InAsSb superlattice absorbers and contact layers and bulk quaternary wide-gap regions. The aim is to reach high detectivity in conditions where the conventional IR photodiodes suffer from a very low quantum efficiency and extremely low resistances due to a high thermal generation of charge carriers. The heterostructures were grown by MBE on GaAs substrates buffered with GaSb. The connections between stages are made using heavily doped narrow-gap p+/n+ tunnel junctions. The room-temperature detectivities of the devices are close to that of immersed MCT multijunction detectors offered by VIGO (PVMI series).
Most photodetectors offered by VIGO are made of mercury-cadmium telluride compound (MCT) by Metalorganic Chemical Vapour Deposition (MOCVD) technology. Despite many advantages of MCT compound, including lattice parameter being almost independent on composition, nowadays in some applications, detectors containing mercury, cadmium and lead are successively removed from the consumer market through norms and directives (e.g. RoHS) due to their toxicity. The abovementioned limitations connected to MCT encouraged the company to find alternative material system and technology as a replacement. Inspired by literature, VIGO decided to develop Ga-free InAs/InAsSb superlattices which are a great candidate, operating in a similar wavelength regime from MWIR to VLWIR. We continue our idea of backside-illuminated devices using substrate material (GaAs) as an immersion lens. We still take advantage of detector material lattice-matched to the buffer layer, replacing CdTe and HgCdTe by GaSb and InAs/InAsSb SL, respectively. The architecture of SLs-based heterostructures originates from MCT photovoltaic devices and utilizes wide bandgap depletion layers for dark current reduction. The detectivity of SL devices is similar to MCT (Fig. 1). Currently, VIGO efforts are focused on the development of HOT LWIR photodiodes including thin absorber devices.
The InAs/InAsSb superlattices are attractive materials for the replacement of both RoHS restricted bulk HgCdTe and strongly Shockley-Read (SR) generation limited InAs/GaSb superlattices. Two main factors limit the performance of InAs/InAsSb photodiodes: the rate of the SR processes, especially in the depletion region, which is the source of the large dark current and a short vertical diffusion length of charge carriers in superlattice absorbers which results in poor responsivity. In this paper, we report on the status of HOT LWIR detectors based on InAs/InAsSb superlattices at VIGO System S.A. The uncooled and Peltier cooled LWIR photoconductors are the most successful devices developed so far. The practical InAs/InAsSb SL-based photoconductors have been fabricated by MBE heteroepitaxial growth on buffered 3” wafers. The design of the devices, material composition and doping, has been optimized for operation at temperatures from 200 to 300 K at a spectral range up to 18 μm. Some of the detectors were supplied with immersion microlenses formed in the GaAs substrates. The devices were characterized by measurements of the spectral responsivity and frequency-dependent noise density. The measured spectral detectivities of the best SL devices were found to be close or better compared to the HgCdTe counterparts operating at the same conditions. The devices are now offered as commercial products. Vigo present efforts are focused on the development of HOT LWIR photodiodes including monolithic cascade devices and thin absorber devices with the plasmonic enhancement of absorption. The development roadmap of advanced HOT devices is also sketched.
This paper reports on the growth details and preliminary characterization of mid-wave infrared radiation InAsSb bariodes. The main device parameters were measured for barrier photodetector heterostructures with three different InAsSb absorber thicknesses: 1 µm (sample no. 1); 1.70 μm (sample no. 2); 2.56 μm (sample no. 3) and one non intentionally doped, 1.70 μm (sample no. 4). The crystallographic structure, responsivity, I-V curves and detectivity characterization were performed.
We report on the investigation of the long term stability study of InAs1-xSbx (x=0.09) high operation temperature (HOT) photodiode grown on GaAs substrate. The electrochemical passivation technique was proposed to modify the mesa sidewalls properties and obtain anodic sulphur coating covered by SU-8 negative photoresist. The dark current densities of sulphur anodic film, SU-8 photoresist and unpassivated devices was compared. Obtained results indicates that the surface leakage current was not fully supressed by unipolar electron barrier. The most stable behaviour after an exposure of 6 months to atmosphere and annealing at 373 K for 72 h was observed for sulphur anodic passivation. This technique turned to be effective also in reduction of oxygen (O) 2s peak in X-ray photoelectron spectroscopy (XPS) in comparison with only etched sample.
The highly Be-doped InAs layer has been grown on semi-insulating GaAs (100) substrate by Molecular Beam Epitaxy. Very good quality of the layer has been attested by high resolution scanning electron microscope (HR-SEM), X-ray diffraction (XRD) and the Raman spectra. The parallel and perpendicular residual strain are determined to be – 1.17 × 10-3 , and 1.12 × 10-3 , respectively. Moreover, the absorbance (ABS) and photoluminescence (PL) spectra were collected in order to estimate the bandgap narrowing. The 10 meV bandgap shrinking for 1.7×1018 cm-3 acceptor concentration suggests necessity of reexamining the Jain et al model [Jain, S. C., et al. - JAP 68(7): 3747-3749] in the context of actual values of InAs valence-bands effective-masses.
We investigate the high-operating temperature performance of InAsSb/AlSb heterostructure detectors with cutoff wavelengths near 5 μm at 230 K. The devices have been fabricated with different types of absorbing layers: nominally undoped absorber (with n-type conductivity), and both n- and p-type doped. The results show that the device performance strongly depends on absorber layer type. Generally, the p-type absorber provides higher values of current responsivity than the n-type absorber, but at the same time also higher values of dark current. The device with the nominally undoped absorbing layer shows moderate values of both current responsivity and dark current. Resulting detectivities D * of nonimmersed devices vary from 2 × 109 to 5 × 109 cm Hz1/2 W ? 1 at 230 K, which is easily achievable with a two-stage thermoelectric cooler. Optical immersion increases the detectivity up to 5 × 1010 cm Hz1/2 W ? 1.
This article reports the parameters and characteristics of recently introduced mid Infrared (3-12um) detection modules for gas sensing applications. In Mid infrared range one can detect almost every simple or complex compound existing on earth. Currently a driving factors for development of gas sensors are related to air/water quality, explosive material detection and medical applications, especially breath analyzers. Gas sensors require source (thermal, diode or laser), sampling compartment and detection module. At VIGO System we are concentrated on designing and manufacturing high operating temperature detectors, fast, sensitive, affordable and reliable required for development of such platforms. We are using active, absorber elements based on complex HgCdTe or InAsSb heterostructures monolithically integrated with optical immersion lens. Additional collective optics, signal amplification, temperature control and heat dissipation will be also discussed in this article. Those functions are critical for ultimate performance of gas sensors.
In this work we investigate the high-operating temperature performance of InAsSb/AlSb heterostructure detectors with cut-off wavelengths near 5 μm at 230 K. The devices have been fabricated with different type of the absorbing layer: nominally undoped absorber, and both n- and p-type doped. The results show that the device performance strongly depends on absorber layer doping. Generally, p-type absorber provides higher values of current responsivity than n-type absorber, but at the same time also higher values of dark current. The device with nominally undoped absorbing layer shows moderate values of both current responsivity and dark current. Resulting detectivities D° of non-immersed devices varies from 2×109 to 7×109 cmHz1/2/W at 230 K, which is easily achievable with a two stage thermoelectric cooler.
In this work we compare two InAs/GaSb superlattice samples grown in MBE VIGO/MUT laboratory on 2 inch (001) GaAs substrate, using MBE technique. Both samples have the same architecture, however their growth processes were conducted at different temperatures. For sample A the growth temperature was equal 668 K (395°C), for sample B 588 K (315°C). Photoluminescence measurements were performed at 30 K. For sample A there is no photoluminescence signal, while spectrum for sample B consists of two peaks: bandgap peak at 0.5 eV and deep state peak at 0.25 eV. X-ray diffraction (XRD) measurements indicate that sample A has better crystallographic quality than sample B. Raman spectra consists of low energy peaks (20-100 cm-1) which confirm the existence of superlattice for both samples [4]. Additionally, for sample A there are peaks related to Sb precipitates. It suggests that except the InAs/GaSb superlattice there is an additional Sb layer which may disturb band structure of superlattice and cause the disappearance of photoluminescence for sample A.
In this work we compare two superlattices: InAs/GaSb (sample A) and InAs/InAsSb (sample B). Both samples were grown in MBE VIGO/ MUT laboratory on 2 inch (001) GaAs substrate using MBE technique. We characterized quality and thickness of the samples using three methods: photoluminescence, X-ray diffraction (XRD) and Raman scattering. Period of superlattice layers was obtained using Raman scattering and XRD measurements. For sample A it was equal 5.3 nm and 4.76 nm for InAs and GaSb layers respectively, for sample B 8.3 nm and 9.4 nm. Photoluminescence spectrum for sample A exhibits two peaks: band gap peak at 0.5 eV and deep state peak at 0.25 eV. Spectrum for sample B consists of one band gap peak at 0.17 eV.
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