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The use of silicon as a substrate alternative to bulk CdZnTe for epitaxial growth of HgCdTe for infrared (IR) detector applications is attractive because of potential cost savings as a result of the large available sizes and the relatively low cost of silicon substrates. However, the potential benefits of silicon as a substrate have been difficult to realize because of the technical challenges of growing low defect density HgCdTe on silicon where the lattice mismatch is ∼19%. This is especially true for LWIR HgCdTe detectors where the performance can be limited by the high (∼5×106 cm−2) dislocation density typically found in HgCdTe grown on silicon. We have fabricated a series of long wavelength infrared (LWIR) HgCdTe diodes and several LWIR focal plane arrays (FPAs) with HgCdTe grown on silicon substrates using MBE grown CdTe and CdSeTe buffer layers. The detector arrays were fabricated using Rockwell Scientific’s planar diode architecture. The diode and FPA and results at 78 K will be discussed in terms of the high dislocation density (∼5×106 cm2) typically measured when HgCdTe is grown on silicon substrates.

In the past several years, we have made significant progress in the growth of CdTe buffer layers on Si wafers using molecular beam epitaxy (MBE) as well as the growth of HgCdTe onto this substrate as an alternative to the growth of HgCdTe on bulk CdZnTe wafers. These developments have focused primarily on mid-wavelength infrared (MWIR) HgCdTe and have led to successful demonstrations of high-performance 1024×1024 focal plane arrays (FPAs) using Rockwell Scientific’s double-layer planar heterostructure (DLPH) architecture. We are currently attempting to extend the HgCdTe-on-Si technology to the long wavelength infrared (LWIR) and very long wavelength infrared (VLWIR) regimes. This is made difficult because the large lattice-parameter mismatch between Si and CdTe/HgCdTe results in a high density of threading dislocations (typically, >5E6 cm−2), and these dislocations act as conductive pathways for tunneling currents that reduce the RoA and increase the dark current of the diodes. To assess the current state of the LWIR art, we fabricated a set of test diodes from LWIR HgCdTe grown on Si. Silicon wafers with either CdTe or CdSeTe buffer layers were used. Test results at both 78 K and 40 K are presented and discussed in terms of threading dislocation density. Diode characteristics are compared with LWIR HgCdTe grown on bulk CdZnTe.

The current-voltage characteristics and quantum efficiencies of double layer planar heterostructure photodiodes were investigated. Results are reported on devices with cutoff wavelengths of 1.8, 2.4, and 3.3 µm. For these respective devices, the dominant currents for temperatures >250,>200,>150K are diffusion currents limited by shallow Shockley-Hall-Read (SHR) processes. The remarkable result is that the electrical and optoelectronic properties of these devices of diverse cut-off wavelength can be explained by simple models using independently measured layer parameters such as the minority carrier lifetimes. For all three cases, the analysis suggests that the same shallow (SHR) centers located at 78% of the energy gap are causing the observed effects. These traps located in then-type base of the device are not influenced by the magnitude of n-type doping and this observation was used to significantly improve the performance of the devices and validate the predictive capability of the models used in the analysis. The shallow centers appear to be process induced rather than grown-in. This assertion is based on the observation that changes in the annealing process led to an order of magnitude improvement in the minority carrier lifetime.

The capability of growing state-of-the-art middle wavelength infrared (MWIR)-HgCdTe layers by molecular beam epitaxy (MBE) on large area silicon substrates has been demonstrated. We have obtained excellent compositional uniformity with standard deviation of 0.001 with mean composition of 0.321 across 1.5″ radii. R0A as high as 5 × 107 ω-cm2 with a mean value of 7 × 106 Θ-cm2 was measured for cut-off wavelength of 4.8 µm at 77K. Devices exhibit diffusion limited performance for temperatures above 95K. Quantum efficiencies up to 63% were observed (with no anti-reflection coating) for cut-off wavelength (4.8–5.4) µm @ 77K. Excellent performance of the fabricated photodiodes on MBE HgCdTe/CdTe/Si reflects on the overall quality of the grown material in the MWIR region.

Results are presented for minority carrier lifetime in n-type molecular beam epitaxy Hg1−xCdxTe with x ranging from 0.2 to 0.6. It was found that the lifetime was unintentionally degraded by post-growth annealing under Hg saturated conditions in a H2 atmosphere that was both time and temperature dependent. This effect was minimal or non-existent for x∼0.2 material, but very strong for x ≥ 0.3. Hydrogen was identified as responsible for this degradation. Identical annealing in a He atmosphere avoids this degradation and results in neartheoretical lifetime values for carrier concentrations as low 1 × 1015 cm−3 in ≥0.3 material. Modeling was carried out for x∼0.2 and x∼0.4 material that shows the extent to which lifetime is reduced by Shockley-Real-Hall recombination for carrier concentrations below 1 × 1015 cm−3, as well as for layers annealed in H2. It appears that annealing in H2 results in a deep recombination center in wider bandgap HgCdTe that lowers the lifetime without affecting the majority carrier concentration and mobility.

The molecular beam epitaxy (MBE) growth technology is inherently flexible in its ability to change the Hg1−xCdxTe material’s bandgap within a growth run and from growth run to growth run. This bandgap engineering flexibility permits tailoring the device architecture to the various specific requirements. Material with active layer x values ranging from ∼0.198 to 0.570 have been grown and processed into detectors. This wide range in x values is perfectly suited for remote sensing applications, specifically the National Polar Orbiting Environmental Satellite System (NPOESS) program that requires imaging in a multitude of infrared spectral bands, ranging from the 1.58 to 1.64 µm VSWIR (very short wave infrared) band to the 11.5 to 12.5 µm LWIR (longwave infrared) band and beyond. These diverse spectral bands require high performance detectors, operating at two temperatures; detectors for the VSWIR band operate near room temperature while the SWIR, MWIR (mid wave infra red), LWIR and VLWIR (very long wave infrared) detectors operate near 100K, because of constraints imposed by the cooler for the NPOESS program. This paper uses material parameters to calculate theoretical detector performance for a range of x values. This theoretical detector performance is compared with median measured detector optical and electrical data. Measured detector optical and electrical data, combined with noise model estimates of ROIC performance are used to calculate signal to noise ratio (SNR), for each spectral band. The SNR are compared with respect to the meteorological NPOESS system derived focal plane. The derived system focal plane requirements for NPOESS are met in all the spectral bands.

Short wave infrared (SWIR) devices have been fabricated using Rockwell’s double layer planar heterostructure (DLPH) architecture with arsenic-ion implanted junctions. Molecular beam epitaxially grown HgCdTe/CdZnTe multilayer structures allowed the thin, tailored device geometries (typical active layer thickness was ∼3.5 µm and cap layer thickness was ∼0.4 µm) to be grown. A planar-mesa geometry that preserved the passivation advantages of the DLPH structure with enhanced optical collection improved the performance. Test detectors showed Band 7 detectors performing near the radiative limit (∼3-5X below theory). Band 5 detector performance was ∼4-50X lower than radiative limited performance, apparently due to Shockley-Hall-Read recombination. We have fabricated SWIR HgCdTe 256 × 12 × 2 arrays of 45 um × 45 µm detector on 45 µm × 60 µm centers and with cutoff wavelength which allows coverage of the Landsat Band 5 (1.5−1.75 µm) and Landsat Band 7 (2.08−2.35 µm) spectral regions. The hybridizable arrays have four subarrays, each having a different detector architecture. One of the Band 7 hybrids has demonstrated performance approaching the radiative theoretical limit for temperatures from 250 to 295K, consistent with test results. D* performance at 250K of the best subarray was high, with an operability of ∼99% at 1012 cm Hz1/2/W at a few mV bias. We have observed 1/f noise below 8E-17 AHz 1/2 at 1 Hz. Also for Band 7 test structures, Ge thin film diffractive microlenses fabricated directly on the back side of the CdZnTe substrate showed the ability to increase the effective collection area of small (nominally

This paper describes recent advances in MBE HgCdTe technology. A new 3 inch production molecular beam epitaxy (MBE) system, Riber Model 32P, was installed at Rockwell in 1994. The growth technology developed over the years at Rockwell using the Riber 2300 R&D system was transferred to the 32P system in less than six months. This short period of technology transfer attests to our understanding of the MBE HgCdTe growth dynamics and the key growth parameters. Device quality material is being grown routinely in this new system. Further advances have been made to achieve better growth control. One of the biggest challenges in the growth of MBE HgCdTe is the day-to-day control of the substrate surface temperature at nucleation and during growth. This paper describes techniques that have led to growth temperature reproducibility within + - 1°C, and a variation in temperature during substrate rotation within 0.5°C. The rotation of the substrate during growth has improved the uniformity of the grown layers. The measured uniformity data on composition for a typical 3 cm × 3 cm MBE HgCdTe/CdZnTe shows the average and standard deviation values of 0.229 and 0.0006, respectively. Similarly, the average and standard deviation for the layer thickness are 7.5 and 0.06 µm, respectively. P-on-n LWIR test structure photodiodes fabricated using material grown by the new system and using rotation during growth have resulted in high-performance (R0)A, quantum efficiency) devices at 77 and 40K. In addition, 128 × 28 focal plane arrays with excellent performance and operability have been demonstrated.

This work presents characterization of implanted and annealed double layer planar heterostructure HgCdTe for p-on-n photovoltaic devices. Our observation is that compositional redistribution in the structure during implantation/ annealing process differs from that expected from classical composition gradient driven interdiffusion and impacts the placement of the electrical junction with respect to the metallurgical heterointerface, which in turn affects quantum efficiency and RoA. The observed anomalous interdiffusion results in much wider cap layers with reduced composition difference between base and cap layer composition. The compositional redistribution can, however, be controlled by varying the material structure parameters and the implant/anneal conditions. Examples are presented for dose and implanted species variation. A model is proposed based on the fast diffusion in the irradiation induced damage region of the ion implantation. In addition, we demonstrate spatial uniformity obtained on molecular beam epitaxy (MBE) material of the compositional and implanted species profile. This reflects spatial uniformity of the ion implantation/annealing Processes and of the MBE material characteristics.

Characterization of defects in Hg1−xCdxTe compound semiconductor is essential to reduce intrinsic and the growth-induced extended defects which adversely affect the performance of devices fabricated in this material system. It is shown here that particulates at the substrate surface act as sites where void defects nucleate during Hg1−xCdxTe epitaxial growth by molecular beam epitaxy. In this study, we have investigated the effect of substrate surface preparation on formation of void defects and established a one-to-one correlation. A wafer cleaning procedure was developed to reduce the density of such defects to values below 200 cm−2. Focal plane arrays fabricated on low void density materials grown using this new substrate etching and cleaning procedure were found to have pixel operability above 98.0%.

We have developed a low temperature procedure for molecular beam epitaxy of CdTe buffer layers on {211} Si wafers and have used Si/ZnTe/CdTe composite substrates for molecular beam epitaxy of double layer Hg1−xCdxTe heterostructures. Planar p-on-n double layer heterostructures were formed by an implantation technique and test diodes were fabricated and characterized. At 77 K, devices with 30×30 μm2 junction area had R0A values in the range 1.5×106–1×107Ω cm2 with a uniform cut-off wavelength of 4.65 μm.

A High Resolution Near-Infrared (NIR) Camera has been developed and tested. This NIR camera uses a HgCdTe detector array which allows for imaging at high operating temperatures. The camera's format is 640x512 pixels with an 18 μm pitch. We have obtained high broadband spectral response from 0.9 to 2.0 micron with near 100% optical fill factor. The camera is designed as a turnkey system that uses the industry standard Camera Link digital interface. The electronics are located remotely from the sensor head allowing it to be adapted to existing optical systems. This compact camera has been targeted for military, scientific and telecommunication applications. This paper will detail the measured camera performance.

Remote sensing applications including the National Polar Orbiting Environmental Satellite System (NPOESS) require imaging in a multitude of infrared spectral bands, ranging from the 1.58 micrometer to 1.64 micrometer VSWIR band to the 11.5 micrometer to 12.5 micrometer LWIR band and beyond. These diverse spectral bands require high performance detectors, operating over a range of temperatures; room temperature for the VSWIR band 100 K for MWIR, LWIR and VLWIR, these needs can all be met using molecular beam epitaxy (MBE) to grow HgCdTe. The flexibility inherent in the MBE growth technology is its ability to vary the HgCdTe material's bandgap within a growth run and from growth run to growth run, a capability necessary for remote sensing applications that require imaging in a wide variety of spectral bands. This bandgap engineering flexibility also permits tailoring the device architecture to the various specific system requirements. This paper combines measured detector optical and electrical data, with noise model estimates of ROIC performance to calculate signal to noise ratio (SNR), D* or noise equivalent temperature difference (NE(Delta) T), for each spectral band. The SNR, D* and/or NE(Delta) T are calculated with respect to system focal plane specifications, as required for the meteorological NPOESS.

The relatively large detector size of conventional focal plane arrays often acts as a limiting source of noise currents and requires these devices to run at undesirably low temperatures. To reduce the detector size without reducing the detector's quantum efficiency, we have developed efficient on-focal plane collection optics consisting of arrays of thin film binary optic microlenses on the back surface of hybrid detector array structures. P/n polarity photodiodes of an unusual `planar-mesa' geometry were fabricated in epitaxial HgCdTe deposited by molecular beam epitaxy on the `front' side of a CdZnTe substrate. Diffractive (8 - 16 phase level) Ge microlenses were deposited on 48 micrometers centers in a registered fashion (using an IR mask aligner and appropriate marks on the front surface of the CdZnTe) on the back side of the substrate using a lifting process. The lifting process circumvents some of the process limitations of the more conventional chemical etching method to diffractive microlens processing, allowing them to approach more closely their theoretical efficiency limit of > 95%. Prior to microlens deposition, but after diode fabrication, the test structures were flip- chip bonded or `hybridized' using indium interconnections to metallic strip lines which had been photolithographically deposited on sapphire dice (a process equally compatible with a silicon integrated circuit readout). After hybridization, the CdZnTe was thinned to equal the focal length of the lenses in the CdZnTe material. Optical characterization has demonstrated that the microlenses combined with the detector mesas concentrate light sufficiently to increase the effective collection area. The optical size of the mesa detectors being larger than the theoretical diffraction limit of the microlenses precludes determining whether the lenses themselves produce the theoretical diffraction-limited gain, but they clearly decrease required detector area by at least 3 - 6X. To our knowledge, this is the first successful demonstration of IR detectors and binary optics microlens integration.

The large detector size of conventional focal plane arrays (FPAs) often acts as a limiting source of noise currents and requires these devices to run at undesirably low temperatures. To reduce the detector size without reducing the detector’s quantum efficiency (QE), we have developed efficient on-focal-plane collection optics consisting of arrays of thin-film binary-optics microlenses and photoresist-based refractive microlenses on the back surface of hybrid detector array structures. Photodiodes of p/n polarity, of an unusual planar-mesa geometry, were fabricated in epitaxial HgCdTe deposited by molecular beam epitaxy (MBE) on the front side of a CdZnTe substrate. Diffractive (8- to 16-phase-level) Ge microlenses were deposited on 48-µm centers in a registered fashion (using an IR mask aligner and appropriate marks on the front surface of the CdZnTe) on the back side of the substrate using a lifting process. The lifting circumvents some of the process limitations of the more conventional chemical etching methods on diffractivemicrolens processing, allowing the microlenses to approach more closely their theoretical efficiency limit of .95%. Photoresist microlenses were fabricated by reflow of photolithographically defined photoresist islands. Prior to microlens deposition, but after diode fabrication, the test structures were flip-chip bonded or ‘‘hybridized’’ using indium interconnections to metallic striplines that had been photolithographically deposited on sapphire dice (a process equally compatible with a siliconintegrated- circuit readout). After hybridization, the CdZnTe was thinned to equal the focal length of the lenses in the CdZnTe material. Optical characterization has demonstrated that the microlenses combined with the detector mesas concentrate light sufficiently to increase the effective collection area. The optical size of the mesa detectors being larger than the theoretical diffraction limit of the microlenses precludes determining whether the lenses themselves produce the theoretical diffraction-limited gain, but they clearly decrease the required detector area by at least 3 to 6 times. To our knowledge, this is the first successful demonstration of IR detectors and binary optics and of photoresist refractive-microlens integration.

Long‐wavelength infrared molecular‐beam epitaxial (MBE) HgCdTe films with dislocation densities as low as 2.3 × 105 cm−2 on (211) GaAs and Si substrates have been obtained by postgrowth thermal annealing and thermal cycle annealing processes (300–490 °C). Experiments show that metalorganic chemical vapor deposition (MOCVD) HgCdTe epilayers require a higher thermal annealing temperature than MBE material and the difference in dislocation reduction between MBE and MOCVD HgCdTe materials is caused by dislocation movement under high‐temperature and thermal stress conditions. The CdTe buffer layer has been observed to play a significant role for the dislocation reduction in the HgCdTe epilayer grown on GaAs or Si alternative substrates. To study the role of dislocations on MBE HgCdTe/GaAs, systematic measurements of the minority carrier lifetime of MBE HgCdTe grown on both CdZnTe and GaAs substrates were carried out. A strong correlation between minority carrier lifetime and dislocation density is observed.

The feasibility of an all molecular‐beam epitaxially (MBE) grown, bias‐switchable, dual‐band HgCdTe detector is demonstrated. Detection in the midwavelength infrared (MWIR) band only or the long‐wavelength band (LWIR) only is accomplished by the proper selection of detector bias in the ≥±100 mV range. The devices were all grown in situ by the MBE on CdZnTe or GaAs substrates and consisted of three intentionally doped layers in an n–p–n sequence. At 77 K the floating base two terminal devices responded to the ∼4.9–8 μm spectral band with the application of ≥−100 mV to the bottom contact and to the ∼2.1–4.9 μm band with the application of ≥0 mV. Quantum efficiency depended on bias with a maximum of 59% for LWIR and 66% for MWIR wavelengths at −150 mV and ≥0 mV, respectively. The operation of the dual‐band detector is discussed. Significant design differences between the heterojunction phototransistor and the dual‐band detector are noted.

A new device concept for CdTe gamma ray detectors has been demonstrated using p+(HgCdTe)-n(CdTe)-n+ (HgCdTe) diode structures. Both P+ and n+ Hg0.25Cd0.75Te epilayers were grown by the liquid phase epitaxy (LPE) technique on semi-insulating CdTe sensor elements. The LPE grown P-I-N structure offers potential advantages for p-n junction and ohmic contact formation over standard ion implanted diodes or Schottky barrier devices. Detectors with active areas of 2 mm2 were fabricated. Resolutions of 10 KeV were obtained for the 122 KeV gamma peak of Co57 at room temperature.

The isothermal vapor‐phase‐epitaxial (ISOVPE) growth of device‐quality HgCdTe layers on both CdTe and CdTe/Al2O3 substrates has been demonstrated. The material and device properties on both types of substrates have been studied and compared with reported values for HgCdTe grown by other techniques. The as‐grown ISOVPE Hg1−xCdxTe (x≂0.3) epilayers are always p type with carrier concentrations of ∼5×1015 to 3×1016 cm−3 and mobilities of ∼230–260 cm2/V s at 77 K. The temperature and compositional dependence of electrical properties of ISOVPE Hg1−xCdxTe are somewhat different from those of liquid‐phase epitaxy (LPE) and bulk HgCdTe. In particular, the acceptor ionization energy, EA =7 meV, is about half that obtained in midwavelength infrared LPE or bulk HgCdTe, and nearly independent of composition x. The R0A product of a representative photodiode (λc ≂4.65 μm, 77 K) is 2×106 and 4 Ω cm2 at 77 and 195 K, respectively, with comparable device qualities seen on both CdTe and CdTe/Al2O3 substrates.

Long and middle wavelength infrared (LWIR, MWIR) p+‐n photodiodes have been fabricated with Hg1−xCdxTe (0.20

Device‐quality Hg1−xCdxTe (0.26

High‐performance backside‐illuminated photodiodes have been fabricated for the first time from InAs1−xSbx‐InAs heterostructures prepared by liquid‐phase‐epitaxy technique. The peak wavelength can be tuned compositionally from 3.1 to over 7.0 μm at 77 K. The half‐width of the spectral responses as narrow as 1760 A (at 4.0 μm) have been achieved. Internal quantum efficiencies of 90% and zero‐bias‐resistance–area products of 2×107 Ω cm2 have been obtained at 77 K.

A planar HgCdTe/CdTe avalanche photodiode with peak responsivity at 1.22 μm and cutoff at 1.25 μm has been fabricated successfully by liquid phase epitaxy (LPE). Avalanche gains of higher than 15 have been obtained with 1.06‐μm Nd:yttrium aluminum garnet (YAG) laser illumination. A reverse breakdown voltage of 80 V and a leakage current density of 1×10−4 A/cm2 at 40 V were measured. The peak quantum efficiency at 1.22 μm is 72% without any antireflection coating.

We report measurements on the minority carrier lifetime in n‐type and p‐type LPE Hg1−xCdxTe/CdTe with x∼0.2. For n‐HgCdTe, we have measured lifetimes of 4–7 μs at 77 K for passivated samples. These values are comparable to the results reported for bulk material. For p‐HgCdTe epilayers with thickness ≤20 μm, the measured lifetime is 15–20 ns at 77 K and is suspected to be limited by surface recombination. With excitation through the CdTe substrate, we have attempted to measure the bulk lifetime; preliminary results are reported.

Infrared photodiodes fabricated with HgCdTe epilayers grown on GaAs substrates by molecular beam epitaxy (MBE) are reported here for the first time. Growth was carried out on the (211)B orientation of GaAs, and the as‐grown epilayer (x=0.24) was p type. The n‐p junction was formed by Be ion implantation, the resistance‐area product (R0 A) at zero bias was 1.4×103 Ω cm2 , the wavelength cutoff was 8.0 μm, and the quantum efficiency was 22%; all were measured at 77 K. We show that in the diffusion regime diodes fabricated with MBE HgCdTe/GaAs have comparable R0 A product values to those made with HgCdTe grown by bulk techniques. This result discloses new possibilities for advanced monolithic HgCdTe devices based on GaAs integrated circuit technology.

Device‐quality Hg1−xCdxTe (0.2≤x≤0.35) epitaxial layers have been grown on CdTe substrates by open‐tube isothermal vapor phase epitaxy (ISOVPE). The surface morphology of the layers is mirrorlike, and the Hall data are comparable to those for HgCdTe grown by liquid phase epitaxy (LPE). Photovoltaic devices with a cutoff wavelength of 4.1 μm at 77 K were fabricated on an ISOVPE HgCdTe epilayer. Their performance is comparable with those that we have obtained for such devices fabricated on LPE HgCdTe epilayers.

A new device structure for room‐temperature gamma ray spectrometry has been developed and demonstrated. The device is a heterojunction p‐i‐n, HgCdTe/CdTe/HgCdTe structure. The p layer is Au doped with NA=1.9×1016 cm−3, μp=35 cm2/Vs, and a Cd composition xCd=0.6. The n layer is In doped with ND=2×1017 cm−3, μn=1880 cm2/Vs, and xCd=0.31. Ohmic contacts were achieved using electron beam evaporated Au (p layer contact) and In (n‐layer contact). Devices (with approximately 2‐mm2 area, 2‐mm thickness) exhibited reverse leakage currents of 50 pA–4 nA, good photovoltaic response with visible light, and voltage breakdowns in excess of 1000 V. At 250‐V reverse bias, the energy resolutions at the principal photopeaks of Am‐241 (60 keV) and Co‐57 (122 keV) were 12.5% and 8.4%, respectively.

Low‐capacitance (< 10 pF) Pb1−xSnxTe photodiodes operating near 77 °K (areas 1.7 × 10−4 cm2) have been obtained via liquid‐phase epitaxial growth of low‐carrier‐concentration material (low 1014 cm−3 to high 1015 cm−3). Response to a mode‐locked 1.06‐μm Nd:YAG laser with the devices terminated in 50 Ω indicated a frequency response to 400 MHz. With a 14‐Ω load and by exciting a photocurrent with radiation from a CO2 laser, the shot noise rolloff point was found to be 1200 MHz. Optimum parameters have not yet been achieved, as evidenced by the increase in frequency response with increase in reverse bias; these results represent only a lower limit to this material's capability.

Hgi-xCdxTe epitaxial layers have been successfully grown in various compositions, for 1-3 μm applications. n+/p junctions are formed either by a standard B-implantation into as-grown p-type layers or by doubly grown p- and n-layers. The SWIR HgCdTe photodiodes exhibit quantum efficiencies of 55-65% without AR coating. For the diodes with 1.39 μm cut-off at room temperature, the zero bias detector resistance-area (RoA) product is 4 x 10 4 Ω-cm2, and the dark current density is ~ 1 x 10 -4 A/cm2 at half-breakdown voltage. The same values of ~ 104 Ω-cm2 RoA products have also been measured for 2.4 μm cut-off photodiodes at 195K. The energy gap and temperature dependence of RoA product is in excellent agreement with the bulk limited generation-recombination model. The breakdown voltages of SWIR diodes vary from 12 volts to greater than 130 volts, depending on the Cd composition (x) and base carrier concentrations.

Experimental liquid crystal 8-12μm infrared modulators have been fabricated and operated utilizing the cholesteric-nematic phase change effect occurring with cyanobiphenyl liquid crystals. A one mil thick film of 4-cyano-4'-pentyl-biphenyl has an average transmission over the whole 8-12μm region of ≈87%. Experiments to determine modulator response times and contrast are discussed as well as some of the basic limitations of infrared modulation using liquid crystals.