The traditional approaches using multiple focal plane arrays (FPAs), filters, beam splitters, cooling circuits etc, complicate system design, reliability and create difficulty in spatial alignment and temporal registration of image at the pixel level. Multiple colors on a single full-resolution FPA will greatly improve spectral discrimination capability at longer ranges. The integrated multicolor infrared FPAs in which a single pixel location is sensitive to two (or three) separate IR spectral bands will be the future generation technology for its use in target acquisition and signature recognition in a wide variety of space and ground based applications. This paper reviews key developments and status of this important technology. Projections and challenges for the continued evolution of this technology are also discussed.

High Performance LWIR Focal Plane Arrays are critical for many space applications. Reliable LWIR focal plane arrays are needed for these applications that can operate in space environment without any degradation. In this paper, we present various LWIR detector array architectures currently being evaluated for LWIR applications. These include backside-illuminated configurations for HgCdTe fabricated on CdZnTe and Silicon substrates. To optimize the LWIR device performance, minimize the anti-reflection losses, and significant reduction in the effects of solarization in space, innovative Anti-reflection coatings are needed, that will enhance the performance of the LWIR detector / focal plane arrays. We also present AR Coating models and experimental results on several promising multi-layer AR coatings that includes CdTe, Si3N4 and diamond like Carbon, that have the necessary spectral response in the 8-14 microns and are hard materials with excellent bond strength. A combination of these materials offers the potential of developing anti-reflection coatings with high optical quality with controlled physical properties.

Multi-color infrared (IR) focal planes are required for high performance sensor applications. These sensors will require multi-color focal plane arrays (FPA) that will cover various wavelengths of interest in MWIR/LWIR and LWIR/VLWIR bands. There has been a significant progress in HgCdTe detector technology for multi-color MWIR/LWIR and LWIR/VLWIR focal plane arrays [1,2,3]. Two-color IR FPA eliminate the complexity of multiple single-color IR FPAs and provide a significant reduction of weight and power in a simpler, reliable and affordable systems. The complexity of multicolor IR detector MWIR/LWIR makes the device optimization by trial and error not only impractical but also merely impossible. Too many different geometrical and physical variables need to be considered at the same time. Additionally material characteristics are only relatively controllable and depend on the process repeatability. In this context the ability of performing simulation experiments where only one or a few parameters are carefully controlled is paramount for a quantum improvement of a new generation of multicolor detectors for various applications. Complex multi-color detector pixels cannot be designed and optimized by using a conventional 1D models. Several additional physical phenomena need to be taken into account. In designing a conventional photovoltaic IR detector array, a trade off exists on the choice of the pixel pitch, the pixel area and its height. The main goal of the device optimization is to reduce the pixel cross talk while keeping a high filling factor and detection efficiency. If the pixel height is made comparable to the lateral pixel dimension the contribution of the lateral photocurrent and lateral generation-recombination current becomes relevant and a full 2D simulation needs to be performed. It also important to point out that the few attempts to perform 2D simulations have reached the conclusion that for advanced IR arrays a full 3D approach should be used. The most challenging aspect of the array design and simulation is the pixel cross-talk effects. Since this is caused by the interaction with the four nearest neighboring pixels, even a description based on a 2D simulation model in most cases is not adequate. It is consequently important to include results from 3D simulation models as a guide to build lower dimensionality models.

High performance large-format Infrared Focal Plane Arrays are required for Third Generation Infrared Imaging technology. HgCdTe IRFPAs exhibit performances to meet this goal. Si-based composite substrates have proven to be the substrate of choice to realize high-resolution HgCdTe arrays. Composite substrate technology offers scalability, and wafer sizes as large as six-inches have been used with excellent compositional uniformity. Current state-of-the-art composite substrates exhibits dislocation density in low to mid 10⁵ cm^-2 range. The HgCdTe epitaxial layers on composite substrates, however, show a defect density in the low to mid 10⁶ cm^-2. Recent developments in CdSeTe/Si composite wafers show great promise for a better lattice matching to HgCdTe alloy, and it is envisioned that with further improvements in both, materials quality and device architecture, a HgCdTe based scalable technology is within our grasp.

This paper reviews and assesses back-illuminated P-on-n photovoltaic HgCdTe detector technology, based on two-layer growth by Liquid Phase Epitaxy on CdZnTe substrates, for application at wavelengths beyond 15 μm in a new generation of spaceborne multispectral instruments for remote sensing. We review data that show feasibility of useful cutoff wavelengths as long as 18-19 μm. We recommend that that LPE photovoltaic HgCdTe technology be extended to the 20-25 μm wavelength region for single elements and small arrays for NASA remote-sensing applications.

Hg1-XCdXTe photodiode arrays have assumed a critical importance for systems requiring sensitivity in any one of the infrared bands of interest extending from the SWIR 1-3 micrometer band to the VLWIR >14 micrometer band. As arrays have become larger, system requirements more stringent and cutoff wavelengths longer, more pressure has been placed on improving the Liquid Phase Epitaxial (LPE) Hg1-XCdXTe growth technique at BAE Systems. In this paper we will report on improvements made in each critical aspect of LPE growth, covering the entire range of Hg1-XCdXTe compositions required for photodiodes with cut-off wavelengths ranging from 3 to greater than 14 micrometers. Data presented will demonstrate that continual advances in LPE Hg1-XCdXTe growth techniques at BAE Systems promise high infrared system performance meeting SWIR to VLWIR needs.

Effective mass ratios, m*, of electrons in near intrinsic and n-type Hg_1-xCd_xTe for 0.20 ⩽ x ⩽ 0.30 over the temperature range 77 K ⩽ T ⩽ 296 K were measured using Faraday rotation spectroscopy. Effective masses were found to be about twice as large at room temperature as band edge effective mass, m*_be, calculations. Measured effective masses diverge further from the theoretical formulations as temperature increases which appears to be due to a thermal excitation effect that is not accounted for in theoretical calculations. These calculations can be corrected using a linear correction factor, m**, where the true effective mass ratio, m* = m** m*_be, where m** was found empirically to be m** = 4.52 x 10^-3 T + 0.78. Carrier concentrations were measured using Hall or van der Pauw tests. Soldered contacts to high mobility materials like HgCdTe using even the purest indium solder inevitably result in contamination that can add significant numbers of impurity carriers to the material and severely decrease mobility. A simple method of burnishing contacts to the material without heat using indium solder is presented. These cold contacts do not effect the material properties and are very effective in n-type HgCdTe making good physically strong contacts that remain ohmic to at least 10 K. This is a review paper.

For the first time, cathodoluminescence of CdSexTe1-x (with x = 0-1) films grown by molecular beam epitaxy on (211) Si substrates were systematically studied and compared with photoluminescence. The Se mole fraction was consistently determined by x-ray rocking-curve diffraction, wavelength-dispersive spectroscopy, and Rutherford backscattering. The band gap energy, as determined by both cathodoluminescence and photoluminescence, was found consistent with literature. The band gap energy varied parabolically with composition as predicted by theory. The results suggest cathodoluminescence can be used to conveniently map composition fluctuations such as Se segregation in CdSe_xTe_1-x films, with higher spatial resolution than photoluminescence.

The fabrication and characterization of heterojunction phtodiodes for room temperature operation in the mid-infrared (2-5 μm) spectral range is described. Liquid phase epitaxy was employed to fabricate two different devices containing In_0.97Ga_0.03As and InAs_0.89Sb_0.11 active regions appropriate for phtodetection at 3.3 μm and 4.6 μm, corresponding to the absorption bands of methane and carbon monoxide. Basic detector characteristics have been measured and were found to compare favourbly with other available detectors in this wavelength range. A simple analystical model was developed to help design and study the corresponding device physics governing the performance of the detectors and was found to give good agreement with the experimentally measured values.

We have developed a range of un-cooled mid-IR LEDs and photodiodes for IR gas sensing applications. Varying the composition of MBE grown Indium Aluminium Antimonide (In_(1-x)Al_xSb) epi-layers on GaAs allows us to engineer the emission/detection wavelength for a particular gas up to λ_max≈6μm. The relatively high series resistance, LED drive requirements, and the non-optimised impedance matching of the un-biased photodiodes restricts the market for these components. Sub-dividing single element devices into N smaller devices connected in series enable the LED current and voltage requirements to be tailored to match the source, and improves the photodiode impedance matching. We report the development of the necessary growth and photolithography technologies for series-connecting InAlSb diodes on GaAs substrates. We include results from multi-element Co₂ (Al(x)=4.5%) and CH₄ (Al(x)=8.5%) sensing LEDs and photodiodes. These impedance matched LEDs represent a 9-fold improvement in the wall-plug efficiency compared with single element LEDs with the same light output. The impedance of the multi-element photodiodes is increased significantly with respect to the series resistance, which gives up to a 5-fold improvement in sensitivity since the noise contributions from the external amplifier and series resistance are minimised. These advances have greatly improved the suitability of these components for gas sensing, and further improvements in the performance are expected through optimisation of the epi-layer design and the device geometry.

InAs photodiodes were prepared by short-term cadmium diffusion into substrates with n-type conductivity. This preparation technique results in formation of p⁺-p-n-n⁺ diodes with compensated region embedded between two doped regions. Experimental data are explained by suppression of Auger recombination in active compensated region. Electrical and photoelectrical properties of photodiodes were investigated in the temperature range 77-295 K. It is shown that the total dark current is determined by the diffusion carrier transport mechanism. The diffused photodiodes exhibit higher photosensitivity in the short wavelength region due to presence of built-in electric field at the surface. Their threshold parameters are found to be approximately the same as in commercially available photodiodes.

The temperature dependence of pyroelectric coefficient in LB films of hemicyanine dyes with different thickness has been investigated. It was found that, in the range from 20 to 45°C, the pyroelectric coefficient was not almost changed for the film thickness less than 32 monolayers. However, the one was enhanced obviously with temperature increasing for the film thickness larger than 32 monolayers. The facts indicated that there is a critical thickness in the ferroelectric LB multilayer films. For the LB films of 20 and 30 monolayers, we can observe two peaks in the temperature dependence of pyroelectric coefficient (at 9 and/or 12°C) under heating and/or cooling processes. But, the heat-hysteresis was not found in 40 monolayers LB films. It is indicated that there are the heat-hysteresis and further confirmed the existence of phase transition in the LB films in the neighborhood of 10°C. It may be demonstrated primarily that the type of phase transition is the surface first-order ferroelectric-paraelectric phase transition by the pyroelectric coefficient measurement.

The phase transition characteristic of the vanadium dioxide (VO2) film prepared by ion beam enhanced deposition (IBED) method was studied. The lattice distortion hypothesis was supposed to simulate resistance change of the VO₂ polycrystalline film with temperature increasing and the simulation result was explained based on Landau theory. Due to the present of argon atom in interstitial site of VO₂ lattice or grain boundary, the semiconductor- to-metal phase transition began at 48°C in some grains, obviously lower than the phase transition temperature of VO₂ single crystal.

Different annealing conditions were adopted to anneal the vanadium oxide films prepared by modified Ion Beam Enhanced Deposition (IBED) method. An X-Ray Diffraction (XRD) was used to analyze the orientation of the IBED films and the resistance was tested with temperature change to measure the Temperature Coefficient of Resistance (TCR). Experiments indicated that there existed a critical temperature for crystallization of VO₂, which changed with the different deposition conditions of the IBED method. It is very difficult to obtain VO₂ structure if the annealing temperature was lower than the critical temperature. If the temperature is much higher than the critical temperature or annealing time is too long, the valence of vanadium in VO₂ film will easily reduce from 4 to low value. The TCR of the IBED VO₂ polycrystalline films annealed in appropriate condition could reach higher than 4%/K.

Recent advances in MEMS and focal plane array (FPA) technologies have led to the development of manufacturing microbolometers monolithically on a readout integrated circuit (ROIC). In this work, both numerical and finite element methods were performed to simulate the transient electrical and mechanical responses of resistive microbolometer FPAs made by several TCR (thermal coefficient of resistance) materials including a-Si, VOx and semiconducting YBCO. Numerical simulation shows that the pulsed bias readout mode in resistive microbolometer FPAs causes a non-steady-state of the system during the operation. As a result, NETD decreases with the increasing pulse width. In FPAs, the array size, frame rate, ROIC and mechanical reliability set the up-limit to the pulse width. The transient mechanical response for three microbolometer configurations was investigated using finite element modeling. The biased pulse results in membrane bending along the z-axis for the symmetric extended configuration (Type I), or twisting in three axes for the asymmetric extended configuration (Type II) due to the constraint force from the supporting arms. The square configuration (Type III) exhibits the smallest deformation and minimum shear stress at the sharp geometries. a-Si microbolometer generates higher shear stress than other microbolometers with the same square configuration.

Electron injection avalanche photodiodes in SWIR to LWIR HgCdTe show gain and excess noise properties indicative of a single ionizing carrier gain process. The result is an electron avalanche photodiode (EAPD) with "ideal" APD characteristics including near noiseless gain. This paper reports results obtained on long-wave, mid-wave, and short wave cutoff infrared HgCdTe EAPDs that utilize a cylindrical "p-around-n", front side illuminated, n+/n-/p geometry that favors electron injection into the gain region. These devices are characterized by a uniform, exponential, gain voltage characteristic that is consistent with a hole-to-electron ionization coefficient ratio, k, of zero. Gains of greater than 1000 have been measured in MWIR EAPDS without any sign of avalanche breakdown. Excess noise measurements on MWIR and SWIR EAPDs show a gain independent excess noise factor at high gains that has a limiting value less than 2. At 77 K, 4.3 μm cutoff devices show excess noise factors of close to unity out to gains of 1000. The excess noise factor at room temperature on SWIR EAPDs, while still consistent with the k = 0 operation, approaches a gain independent limiting value of just under 2. The k = 0 operation is explained by the band structure of the HgCdTe. Monte Carlo modeling based on the band structure and scattering models for HgCdTe predict the measured gain and excess noise behavior. A noise equivalent input of 7.5 photons at a 10 ns pulsed signal gain of 964, measured on an MWIR APD at 77 K, provides an indication of the capability of the HgCdTe EAPD.

We have developed high-speed germanium (Ge) photodetectors using standard complementary metal-oxide-semiconductor (CMOS) process technology. We describe the design considerations that led to the devices reported on here. We have characterized these detectors in terms of the following detector metrics: speed, responsivity, dark current and capacitance. The photodetectors exhibit responsivities greater than 0.2 A/W at both 850 and 1550 nm, making them compatible with both long- and short-haul communication systems. Impulse response measurements at both of the above wavelengths indicate 3 dB cutoff frequencies greater than 10 GHz and open eye diagrams have been measured at 20 Gb/s. Dark currents are on the order of 10 to 1000 μA at a bias of 1 V depending on device size. Capacitances measured were on the order of 0.1-10 fF. The performance of the detectors indicates that they are suitable for high speed on-chip optical links. Device simulation models indicate that the fundamental upper limit on the speed of the devices, based on ideal material properties, is high enough to support a number of process generations. Calibration of the models to our experimental data is presented, and areas for improvement are defined.

We report MOVPE-grown quantum cascade lasers with operating wavelengths between λ~7.5-9.5μm with threshold current densities as low as 2.4kA/cm2 at room temperature. Seven wafers grown for operation at ~9μm show a variation of just 3% in the superlattice periods obtained from X-ray analysis, and laser emission is observed from all wafers with a ~5meV spread of emission energies. Multimode Fabry-Perot and singlemode distributed feedback lasers have been fabricated, operating at λ~7.8μm at room temperature, corresponding with absorption lines in the infrared spectra of methane. In addition, we have produced a strain compensated MOVPE-grown quantum cascade laser operating at λ~4.5μm.

The transportation community has applied sensors for various traffic management purposes, such as in traffic signal control, ramp metering, traveler information development, and incident detection by collecting and processing real-time vehicle position and speed. The U.S. transportation community has not adopted any single newer traffic detectors as the most accepted choice. The objective of this research is to develop an infrared sensor system in the laboratory that will provide improved estimates of vehicle speed compared to those available from current infrared sensors, to model the sensor’s failure conditions and probabilities, and ultimately refine the sensor to provide the most reliable data under various environmental conditions. This paper presents the initial development of the proposed sensor system. This system will be implemented in a highway segment to evaluate its the risks of failure under various environmental conditions. A modified design will then be developed based on the field evaluations.

The porous silicon deserves great scientific attention due to intensive photoluminescence can be observed at the room temperature. With the purpose of modeling photo-electric properties of porous silicon the researches of influence of non-uniform deformation of silicon monocrystal on the form of spectral distribution of photoconductivity were carried out. Measurements of the photoconductivity (PC) and photomagnetic effect (PME) spectra of crystalline silicon were carried out for the sample under the non-uniform bend deformation. This deformation causes a decrease of the photoconductivity spectrum drop in the short-wave region when illuminating the stretched surface. Under constant deformation conditions the PME spectrum form is changed only in the long-wave region. Obtained data are explained by diffusion length decreasing as a consequence of decreasing diffusion coefficient under the influence of a strain gradient. The analysis of the investigated photo-electric properties of porous silicon has resulted in a conclusion about the excitation photoluminescence occurs in amorphous matrix of porous silicon. And the important role plays drift of nonequilibrium carriers of a charge in an internal electrical field of porous silicon at carry of energy the excitation from area of generation to the centre of luminescence. The work has excellent application for production of porous silicon based photodiodes with improve performances.

Mid wavelength infrared (MWIR) HgCdTe heterostructures were grown on 3-inch dia Si (211) substrates by the molecular beam epitaxy technique and p+n format devices were fabricated by arsenic ion implantation. Very long wavelength infrared (VLWIR) layers have been employed as interfacial layers to block the propagation of detects from the substrate interface into the HgCdTe epilayers. Excellent material characteristics including the minority carrier lifetime of 7.2 usec at 200K and 2 usec at 80K in the n-HgCdTe absorber layer with 5 um cut-off wavelength at 80K were achieved. The photovoltaic detectors fabricated on these MWIR heterostructures show excellent zero-bias resistance-area product (R0A) on the order of 10⁸ ohm-cm² and peak dynamic impedances on the order of 109 ohm-cm². A two-step arsenic activation anneal followed by the 'Hg' vacancy filling anneal (third step) is shown to produce the best R0A values, since the intermediate temperature annealing step seems to control the diffusion of arsenic, assisted by the implantation-induced defects. The experimental R0A values are compared with that predicted by theory based on a one-dimensional model, indicating g-r limited performance of these MWIR devices at 80K.