Raytheon Vision Systems (RVS) in collaboration with HRL Laboratories is contributing to the maturation and manufacturing readiness of third-generation two-color HgCdTe infrared staring focal plane arrays (FPAs). This paper will highlight data from the routine growth and fabrication of 256x256 30μm unit-cell staring FPAs that provide dual-color detection in the mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) spectral regions. FPAs configured for MWIR/MWIR, MWIR/LWIR and LWIR/LWIR detection are used for target identification, signature recognition and clutter rejection in a wide variety of space and ground-based applications. Optimized triple-layer-heterojunction (TLHJ) device designs and molecular beam epitaxy (MBE) growth using in-situ controls has contributed to individual bands in all two-color FPA configurations exhibiting high operability (>99%) and both performance and FPA functionality comparable to state-of-the-art single-color technology. The measured spectral cross talk from out-of-band radiation for either band is also typically less than 10%. An FPA architecture based on a single mesa, single indium bump, and sequential mode operation leverages current single-color processes in production while also providing compatibility with existing second-generation technologies.

The cost and performance of hybrid HgCdTe infrared focal plane arrays are constrained by the necessity of fabricating the detector arrays on a CdZnTe substrate. These substrates are expensive, fragile, are available only in small rectangular formats, and are not a good thermal expansion match to the silicon readout integrated circuit. We discuss in this paper an infrared sensor technology based on monolithically integrated infrared focal plane arrays that could replace the conventional hybrid focal plane array technology. We have investigated the critical issues related to the growth of HgCdTe on Si read-out integrated circuits and the fabrication of monolithic focal plane arrays: (1) the design of Si read-out integrated circuits and focal plane array layouts, (2) the low temperature cleaning of Si(001) wafers, (3) growth of CdTe and HgCdTe layers on read-out integrated circuits, (4) array fabrication, interconnection between focal plane array and read-out integrated circuit input nodes and demonstration of the photovoltaic operation, and (5) maintenance of the read-out integrated circuit characteristics after substrate cleaning, molecular beam epitaxy growth and device fabrication. Crystallographic, optical and electrical properties of the grown layers are presented. Electrical properties for diodes fabricated on misoriented Si and read-out integrated circuit substrates are discussed. The fabrication of arrays with demonstrated I-V properties show that monolithic integration of HgCdTe-based infrared focal plane arrays on Si read-out integrated circuits is feasible and could be implemented in the 3^rd generation of infrared systems.

SWIR HgCdTe photodiode test chips and 256x256 Focal Plane arrays with a 2.1 micron cutoff wavelength have been fabricated and tested. The base material was n-type HgCdTe. P-type junctions were created by ion implantation. Test chip arrays with 60-micron pixels exhibited an average R_oA of 509 ohm-cm² and internal quantum efficiency (QE) of 98% at 295 K; R_oA and QE were uniform. Average R_oA increased to 2.22x10⁴ at 250 K and internal QE remained high at 93%. The mini-array of 30-micron pixels had lower R_oA values, 152 and 6.24x10³ ohm-cm2 at 295 and 250 K, but 100% internal quantum efficiency at both temperatures. There was no bias dependence of quantum efficiency, demonstrating that our junction formation process does not give rise to valence band barriers. FPA test data have demonstrated NEI operability greater than 98% at 220 K and greater than 97% at 250 K along with QE operability in excess of 99.9% at 220 K and in excess of 99.8% at 250 K.

In this paper a model for thermosolutal convection, thermotransport and mass transport is considered for a Bridgman-Stockbarger growth system. It is shown that if the growth process takes place in zero- gravity or in a low gravity environment and if at the moment when the bottom of the ampoule enters into the gradient zone the dopant concentration in the melt is given by a certain formula, then in the first 70% of the grown crystal the dopant concentration is almost equal to a prescribed concentration. In practice this means that the ampoule has to be filled with thin concentric rings, obtained by compacting powder, each of these rings having a constant concentration of dopant, given by the formula in function of the position of the ring in the ampoule. This ampoule is introduced into the hot zone of the furnace and the content is melted quickly so that the dopant diffusion during the melting process can be neglected. At the end of the melting process the translation of the ampoule begins. Numerical results are given to show the computed improvement obtainable in comparison to the experimental results.

The growth and characterization of Au-doped HgCdTe layers on (211)B CdTe/Si substrates grown by molecular beam epitaxy reported. The electrical properties of these layers studied for diffusion are presented. For ex-situ experiments, thin Au layers were deposited by evaporation and annealed at various temperatures and times to investigate the p-type doping properties and diffusion of Au in HgCdTe. The atomic distribution of the diffused Au was determined by secondary ion mass spectroscopy. We found clear evidence for p-type doping of HgCdTe:Au by in-situ and ex-situ methods. For in-situ doped layers, we found that, the Au cell temperature needs to be around 900°C to get p-type behavior. The diffusion coefficient of Au in HgCdTe was calculated by fitting SIMS profiles after annealing. Both complementary error functions and gaussian fittings were used, and were in full agreement. Diffusion coefficient as low as 8x10^-14cm²/s observed for a sample annealed at 250°C and slow component of a diffusion coefficient as low as 2x10^-15 cm²/s observed for a sample annealed at 300°C. Our preliminary results indicate no appreciable diffusion of Au in HgCdTe under the conditions used in these studies. Further work is in progress to confirm these results and to quantify our SIMS profiles.

P⁺-v-N⁺ structures with HgTe/CdTe superlattice absorber regions were grown by MBE to give cut-off wavelengths in the very long wavelength infrared (14 μm and longer) at temperatures below 80 K. The superlattice period of one sample was 98.3Å according to its x-ray diffraction profile, very close the intended 98.5Å for a 48.5Å HgTe/50.Å Hg_0.05Cd_0.95Te superlattice. The cut-off wavelengths of another sample were approximately 14 and 18 μm at 77 and 40K, respectively, as determined by optical absorption and spectral response measurements. A first batch of devices annealed at 150°C or 180°C for 1 hr after the deposition of 50Å thick gold films showed relatively low R₀A values (approximately 0.3 ohm-cm²). This was interpreted to be due to the formation of a junction near the boundary of the superlattice and a high carrier concentration region of HgCdTe alloy. A second batch of devices was annealed at 120°C for 1 hr or 5 min. to decrease the gold diffusion depth. The electrical properties showed higher R₀A values (approximately 8 ohm-cm²). The detectivities of the second batch devices at 77K were in the range of 10⁸ to 10¹⁰ cmHz½/W and showed frequency dependence because the noise had frequency dependence. We observe very low knee frequencies (below 10Hz) in their noise spectra.

We examine the potential of (211) HgTe/CdTe superlattices for applications involving the detection of very long wavelength infrared radiation (cut-off wavelengths longer than 15μm at 40K). The superlattice electronic band structures and radiative and Auger recombination rates were theoretically modeled. The layer widths were optimized to suppress Auger recombination. Several of the theoretically designed superlattices were grown to 200 periods on (211)CdTe/Si substrates and characterized. Both the layer widths and crystal quality were determined by means of x-ray diffraction measurements. The temperature dependent absorption coefficient was measured to determine the cut-off wavelengths. Theory and experiment are in close agreement for energies above 60meV. Reliable experimental data could not be extracted below 60 meV, however the computed H1-E1 energies are useful assessments of the actual cut-offs. We also present transmission electron microscopy images and secondary ion mass spectroscopy data of the grown superlattices. Our results demonstrate the feasibility of using superlattices in very long wavelength infrared detector structures.

Very long wavelength infrared (VLWIR, λ_c approximately 20 to 50 μm) HgTe/HgCdTe superlattices were grown by molecular beam epitaxy (MBE). The layers were characterized by means of X-ray diffraction and Fourier transform infrared spectroscopy. Photoconductive interdigitated electrode detectors for heterodyne applications in the Far-infrared wavelengths (FIR) regions were designed and fabricated. Spectral response measurements exhibit the ability of these detectors to function in the long wavelength (LWIR) to VLWIR regions. Detectivity observed at 77 K is very encouraging and could be enhanced further at lower operating temperatures.

The technology for the small-size focal plane arrays and linear arrays of polycrystalline SiGe microbolometers is developed at IMEC and successfully transferred to its industrial partner XenICs. A NETD of about 100 mK is achievable at the readout level on 14×14 and 200×1 arrays with 50 - 60 μm pixel pitch at a time constant of 20 - 25 ms. The design of pixels provides very precise tuning of the infrared resonant cavity. The resistance and TCR nonuniformity with σ/μ better than 0.2% combined with about 1% noise nonuniformity and 100% pixel operability are demonstrated. The first lot of arrays has been characterized, the arrays have been assembled with hybrid readout chips, supplied with the dedicated evaluation board and a software, and the results of system testing are being reported. The possibility to use the SiGe arrays as infrared emitters has been investigated for the first time and the results are presented as well.

The special technology of development of pyroelectric detectors on a base of the systems "thin Pd film -- thick lithium niobate substrate" is proposed. The processing of such system by Ar⁺ ions is proposed for improving some characteristics of material for pyroelectric detector. The optimal Pd film thicknesses as well as ions energies and doses were calculated by Monte-Carlo method for reaching appropriate sensitivity and response of pyroelectric detectors. Investigation of surface structure of the systems by electronic microscopy and AFM method has shown that structural changes of the researched materials depend on film's material and its properties. This result is confirmed by ellipsometric study of the systems. The optical properties of nonimplanted and implanted systems "thin Pd film -- thick lithium niobate substrate" are investigated in the wide spectral range (200 nm - 15 μm). It is shown that the reflectance of the implanted system is nonselective in the infrared. The adhesion and antidegradation stability of metal films on bulk lithium niobate increase after implantation. The selection criteria for finding of appropriate film materials for application in modern optoelectronic devices are proposed.

Low cost germanium photodetectors for sensing applications in the 900-1600 nm spectral region have been developed. By varying the Ge substrate resistivity as well as device area, photodetector properties such as reverse leakage current, capacitance, and shunt resistance have been engineered. Low leakage current devices of various sizes up to 1 cm² have been fabricated and have consistently exhibited exceptionally high shunt resistances and excellent linearity. Over 5000 hours of active stress testing have left the ultra-low leakage currents unchanged. These data were measured in accordance with Telcordia 468-CORE requirements at 85°C, 125°C and 175°C. The results indicate that these mesa photodetectors meet telecommunication industry requirements for reliability. These devices are comparable to commercially available Ge photodetectors, and can be readily substituted for more complex InGaAs photo-detectors in applications such as laser monitor diodes.

Pyroelectric detectors of infrared radiation are fast-response thermal sensors operating at ambient temperature unlike semiconductor detectors, which require cooling. Their spectral response is uniform in a large range of wavelengths, including the main band of IR transmission within the earth's atmosphere. A further increase in pyroelectric response is possible by integrating pyroelectric sensors with silicon technology. Triglycine sulfate (TGS) based pyroelectric detectors are the most sensitive among available ferroelectric materials. Efforts made so far in improving their growth yield, mechanical properties and figures of merit for their use, as infrared detectors will be presented. Effective sensitivity and performance depend not only on the pyroelectric sensor element material characteristics, but also on the thermal performance of the complete structure of a detector, such as substrate material (Si), absorbing layer, and isolation layers including associated electronics. Thus, we have calculated the thermal transfer function by solving a one-dimensional thermal diffusion equation for a single element n-layer structure. From which the performance of any number of layers detector structure can be derived, predicted, and optimized. Using various single sensor configurations and pyroelectric parameters of modified TGS crystals grown in our laboratory; the calculated and predicted repsonsivity and other parameters of integrated detector system will be presented. The results obtained are encouraging for the development of TGS thin film based detectors.

We have developed surface micromachined Infrared ray (IR) focal plane array (FPA), in which single SiO₂ layer works as an IR absorbing plate and Pb(Zr_0.3Ti_0.7)O₃ thin film served as a thermally sensitive material. There are some advantages of applying SiO₂ layer as an IR absorbing layer. First of all, the SiO₂ has good IR absorbance within 8 ~ 12 μm spectrum range. Measured value showed about 60% absorbance of incident IR spectrum in the range. SiO₂ layer has another important merit when applied to the top of Pt/PZT/Pt stack because it works also as a supporting membrane. Consequently, the IR absorbing layer forms one body with membrane structure, which simplifies the whole MEMS process and gives robustness to the structure.

Intermixing effects of MOCVD (metal organic chemical vapor deposition) grown InGaAs SAQDs (self-assembled quantum dots) covered with SiO₂ and SiN_x-SiO₂ dielectric capping layers were investigated. The intermixing of SAQDs was isothermally performed at 700°C by varying annealing time under the N₂-gas ambient. It was confirmed from the PL measurement after the thermal annealing that, the emission energy of SAQDs was blue-shifted by 190 meV, the FWHM (full width at half maximum) was narrowed from 76 meV to 47 meV and the PL intensity was increased. SiNx-SiO₂ double capping layer have been found to induce larger PL intensity after the thermal annealing of SAQDs compared to SiO₂ single capping layer. The results can be implemented for increasing quantum efficiency and tuning the detection wavelength in quantum dot infrared photodetector (QDIP).

Thermoelectric Coolers (TEC's) are reversible heat pumps which can be employed for cooling and/or temperature stabilization of critical electronic circuits which might become in-operable without removal of the heat generated within the device. Thermoelectric temperature stabilization is often used in uncooled Infrared imaging systems due to the temperature sensitive nature of the detector array. These Infrared systems operate in environments where the ambient temperature changes. The TEC is used to either heat or cool the detector array to its optimized temperature. The integrated TEC concept involves soldering of individual thermoelectric elements directly in the base of the package. The package is made from metallized multi-layer ceramic which includes electrical pins for both the TEC and the detector array. Integrating the cooler directly into the package offers many advantages. It reduces the number of piece parts in the system, the number of soldering or bonding operations, allows for a higher temperature assembly, and eliminates the TEC mounting operation for detector manufacturers. The integrated TEC can be designed to meet operative parameters such as power, temperature delta, slew rate, size, and robustness. The purpose of this document is to provide assistance to design engineers on key design parameters and considerations when including an integrated thermoelectric cooler into the assembly.

In a smart weapon system, reliability of the sensor system is the most essential characteristic. Self Test (ST) is a way to diagnose the health of the system in order to keep the system reliable. It is important to measure reliability not only right before system deployment but also during the system development. For a robust self test design, many things need to be addressed. One important consideration is a way to input threshold values without code change to the released self test. Threshold values can be ever changing measuring sticks depending on each sensor's characteristics or material changes during the development of sensors. Another consideration is a way to do fault isolation to enable component replacement. In this paper, we will present how we have built a robust self test for the MMS. In the conclusion, lessons learned will be shared.

Photocathode based on GaAs/AlGaAs heterojunction has been applied broadly in night vision imaging intensifiers for its broad spectral response wavelength, high quantum efficiency and low dark current. Especially in recent years the extension of response wavelength to near infrared makes GaAs/AlGaAs applied in laser imaging. To obtain negative electron affinity GaAs photocathode with high performance, reasonable selection of performance parameters of GaAs material is required. In this paper on basis of photoemission model, analysis of the influences of diffusion length of minor carrier, recombination velocity at the interface of GaAs/AlGaAs and thickness of active GaAs layer on spectral response of GaAs photocathode were detailed, and the optimizing principle and methods of these parameters were proposed. Our measurement results of compositions distributions of GaAs/AlGaAs heterojunction are also given to demonstrate influences of material performance parameters.

Spectral response curves of photoemission materials and spectral matching factors between detectors and reflecting spectrum of scenes are of importance in the study of detectors and imaging devices. For studying the two questions an automatic spectral recording system was developed and the schematic diagram of the system was demonstrated in this paper. A lot of experiments by use of the system were made to obtain spectral response curves and characteristic parameters of multi-alkali and GaAs:Cs-O photocathodes during activation procedure and these experimental results were given. It was found that electron affinity of Na₂KSb, Na₂KSb+Cs and [Na₂KSb+Cs]+Sb+Cs multi-alkali photocathodes were 0.70-0.91eV, 0.35-0.41eV and 0.33eV respectively calculated from threshold wavelength of spectral response curves and quantum yield during preparation. On-line spectral response measurements of GaAs:Cs-O reflection-mode photocathodes during activation process and decay procedure were carried. The prepared GaAs:Cs-O reflection-mode photocathodes which used national p-type GaAs substrate can obtain 1025μA/lm sensitivity.

Infrared radiometry requires large area, linear detectors of spatially uniform response. Currently the choice of high quality detectors of mid-infrared (>8 μm) radiation is far from ideal for radiometric applications. For example, HgCdTe detectors are widely used but exhibit very large (>20%) spatial non-uniformities in their responsivity whereas thermal detectors such as pyroelectric detectors have relatively low D* values. Quantum Well Infrared Photo-detectors (QWIPs) are now well established for use in state-of-the-art cooled thermal imaging systems, driven by military application. For fundamental optical measurement applications (for example, spectral responsivity standards) the expense and complication of imaging arrays is not required. Some QWIPs are made from layers of GaAs/Al_xGa_1-xAs material which can be mass grown on large substrate wafers with high spatial uniformity. As such, QWIPs offer the potential to be manufactured as a large area single pixel device, with a uniform spatial response, as well as a high D* value. This paper will detail the development of a single pixel QWIP detector and present the results of an initial evaluation of this detector, carried out at NPL.

In its role as the national standards laboratory for the UK, the National Physical Laboratory (NPL) maintains, develops and disseminates, amongst others, the UK's detector spectral responsivity scale and material spectrometric scales (regular, hemispherical and angular reflectance and transmittance). In order to carry this work out detectors, materials, methods and facilities are continually under development at NPL. This paper will present the latest measurement techniques used at NPL that are applicable for the characterisation of infrared detectors and materials. NPL has extensive calibration capabilities, making use of grating and FT spectrometers and tuneable lasers, covering a wide spectral range, catering for single element, array, sub-pixel resolution and photon counting devices. As well spectral responsivity, detector spatial uniformity and linearity measurements are available. The UK spectrometric scales are maintained from 200 nm to 56 μm and include regular, hemispherical and angular reflectance and transmittance scales, and artefacts for the wavenumber and ordinate calibration of mid-infrared spectrometers.

The studies of the optical and photoelectric properties of Cd_1-xHg_xTe:V (x≤0.02, N_v = 10¹⁹ cm^-3) were carried out. The investigated semiinsulating (ρ = 10⁸ - 10⁹ Ωxcm) crystals were grwn by the vertical Bridgman technique. All obtained samples had n-type conductivity. The measurements of absorption, photoluminescence and photodiffusion spectra allowed us to obtain the information about the impurity centers and intrinsic defects. The nature and the position of their energy levels with respect to the crystal energy band were determined. It was shown that the impurity centers are in the two- and three-ionized states. In the case of V²⁺ ions excited ⁴T₁(F)- and ⁴A₂(F)-states for Cd_1-xHg_xTe:V (x =0.018) crystal is in resonance with the conduction band. It was found that for these crystals the photogeneration of electrons from impurity levels are determined both by direct photoionization and autoionization of electrons from excited states to the conduction band. It was found that the photosensitivity region for Cd_1-xHg_xTe:V crystals is protracted up to 1800 nm. The dynamic of electronic processes with the participation of impurity and intrinsic defects were investigated using a time-resolved photoelectric spectroscopy. It was shown that the electric processes, which determine the photosensitivity region of this crystal is high speed and corresponds to the subnanosecond region.

Transition Edge Sensor (TES) quantum microcalorimeters can provide intrinsic arrival time and energy resolved measurements of individual photons over a large energy range centered on the optical band. Our TESs consist of thin-film superconduting tungsten pixels on a silicon substrate. The pixels are voltage-biased to remain in the sharp superconducting transition region through negative electrothermal feedback. We report progress on our first imaging TES array of 32 pixels. We describe the experimental apparatus, summarize recent progress, characterize detector performance and outline the future path of TES development.