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Minority-carrier lifetimes and diffusion lengths have been deduced from a comparison of band structure simulations and experimental measurements on mid-wave infrared InAsSb XBn and long-wave infrared InAs/GaSb type II superlattice (T2SL) XBp barrier detectors with low diffusion-limited dark current close to mercury cadmium telluride Rule 07 and high quantum efficiency. For the XBn devices, a lifetime of 1.9 μs was observed with a corresponding diffusion length of 14.5 μm. In contrast, the T2SL exhibited a much shorter lifetime of 7.5 ns, but the diffusion length of ∼ 7 μm was long enough to ensure that almost 90% of the photocarriers are collected. The lifetime appears to be Auger limited in the case of n-type InAsSb, but for the p-type T2SL, Shockley–Read–Hall (SRH) traps appear to dominate. In the second case, possible scenarios for the dominance of SRH recombination are discussed to identify pathways for further performance optimization.

The minority carrier lifetime in p-type InAs/GaSb type II superlattices (T2SLs) is quite short, typically in the region of tens of nanoseconds. In spite of this, T2SLs are becoming a viable alternative to Mercury Cadmium Telluride as the sensing material of choice for high end MWIR and LWIR infrared detectors. For example, SCD now manufactures a 640 × 512 format, 15 μm pitch LWIR focal plane array detector, with a quantum efficiency close to 50%, a pixel operability of >99.5%, and a dark current only about one order of magnitude larger than the state of the art Rule 07 value. A key to the very high performance of this detector is the use of an XBp barrier architecture that both suppresses the G-R current and allows stable passivation to all steps of the fabrication process. Since both the dark-current and photo-current in the XBp structure are diffusion limited, measurements of these quantities as a function of the device dimension provide an excellent vehicle for estimating the minority carrier lifetime and diffusion length, when performed in conjunction with k⋅p calculations of the T2SL density of states. Typical lifetime results are presented, which are consistent with values found by others using direct measurements. Diffusion lengths are reported in the range 3–7 μm, although these are not necessary limiting values.

Semi-Conductor Devices’ long-wave infrared 640 × 512/15-μm pitch type II superlattice detector is based on an XBp design with an InAs/GaSb absorbing layer and an InAs/AlSb barrier layer. The barrier architecture ensures a low, diffusion-limited, dark current and allows stable passivation to all fabrication steps. It is shown that the dark current is about 10 times the Rule 07 value and corresponds to a minority carrier lifetime of about 10 ns, while the quantum efficiency can approach within 10% of the HgCdTe value for realistic detector parameters. Detectors are now being manufactured with a reasonable yield for an operability above 99.5%, and a stable and reproducible noise equivalent temperature difference of

Introduction: Diagnostic IBD practice has been affected by COVID-19, with>50% of new diagnoses not having endoscopy in a UK nationwide study.1 A case series of delayed presentation of surgical complications related to IBD has been reported in Italy.2 We report a case of delayed diagnosis of severe Crohn's disease due to the pandemic. Case Description/Methods: 57 year old woman was seen for chronic diarrhea of two months duration in January 2020. Her past medical history is noted for type 2 diabetes. Patient reported foursix liquid bowel movements daily associated with severe abdominal pain in the lower abdomen unaffected by eating. Infectious evaluation was negative. A CT Abdomen without contrast in January 2020 showed terminal ileitis with a hazy infiltration of the fat and thickened small bowel loops suggestive of enteritis. Her fecal calprotectin and CRP were both elevated at 846 ug/g and 4.2 mg/dl, respectively. Patient was planned and scheduled for colonoscopy with random biopsies and terminal ileum intubation and small bowel capsule endoscopy. The planned procedures were deferred due to the pandemic as endoscopy services were not available at our institution between March 2020-July 2020. Patient was lost to follow-up until December 2020;patient expressed fear of receiving care amidst the pandemic. Colonoscopy in March 2021 was unremarkable endoscopically and histologically with difficulty in intubating the terminal ileum due to anatomy. Small bowel capsule endoscopy in March 2021 showed several aphthous ulcers and significant enteritis with diffuse ulcerations in the small bowel (Figure 1A-C). The findings are highly suggestive of Crohn's disease. Patient underwent CT Enterography in May 2021 that showed mucosal edema with wall thickening of the terminal ileum (Figure 1D). Patient is planned for biologic therapy for suspected small bowel Crohn's disease. Discussion: Our case report describes a case of delayed diagnosis of Crohn's disease due to unavailability of endoscopy services and patient-related factor of fear of the pandemic. Future studies should evaluate for any diagnostic delay in IBD care in the United States.

A photodetector based on InAs/InSb/AlSb type-II superlattice (T2SL) with thicknesses of 15, 1 and 4 monolayers respectively, was fabricated and characterized. The interface between InAs and AlAs of one InSb monolayer, increases the λ cutoff to 3.3 μm, and improves the InAs/AlSb layer correlation and strain balancing. With a −0.5 V bias, the dark current at 300 and 200 K was 1.1 and 8.5 × 10 − 3 A/cm 2 respectively, and the quantum efficiency at λ = 2.75 μm, for both 300 K and 200 K, was 34%. The detectivity was above 10 9 cm-Hz 1/2 /W for 300 K and above 10 10 cm-Hz 1/2 /W for 200 K between 2.5 and 3 μm wavelength.

XBn or XBp barrier detectors exhibit diffusion-limited dark currents comparable with mercury cadmium telluride Rule-07 and high quantum efficiencies. In 2011, SemiConductor Devices (SCD) introduced “HOT Pelican D”, a 640 × 512/15-μm pitch InAsSb/AlSbAs XBn mid-wave infrared (MWIR) detector with a 4.2-μm cut-off and an operating temperature of ∼150 K. Its low power (∼3 W), high pixel operability (>99.5%) and long mean time to failure make HOT Pelican D a highly reliable integrated detector-cooler product with a low size, weight and power. More recently, “HOT Hercules” was launched with a 1280 × 1024/15-μm format and similar advantages. A 3-megapixel, 10-μm pitch version (“HOT Blackbird”) is currently completing development. For long-wave infrared applications, SCD’s 640 × 512/15-μm pitch “Pelican-D LW” XBp type II superlattice (T2SL) detector has a ∼9.3-μm cut-off wavelength. The detector contains InAs/GaSb and InAs/AlSb T2SLs, and is fabricated into focal plane array (FPA) detectors using standard production processes including hybridization to a digital silicon read-out integrated circuit (ROIC), glue underfill and substrate thinning. The ROIC has been designed so that the complete detector closely follows the interfaces of SCD’s MWIR Pelican-D detector family. The Pelican-D LW FPA has a quantum efficiency of ∼50%, and operates at 77 K with a pixel operability of >99% and noise equivalent temperature difference of 13 mK at 30 Hz and F/2.7.

A molecular beam epitaxy-grown InGaAsSb p–n photodetector lattice matched to GaSb for extended short wave infrared is reported. Electrical and optical characteristics were analyzed at temperatures from 200 K to room temperature. The photodetectors exhibit dark current densities of 2.9 × 10−6 A/cm2 at 200 K and 4.6 mA/cm2 at 300 K (−0.1 V bias) and a high quantum efficiency of 73% at room temperature under front side illumination. High detectivity (D*) values of 2.2 × 1010 cm·Hz1/2 W−1 and 7.4 × 1011 cm·Hz1/2 W−1 were observed at 200 K and room temperature, respectively.

We studied InAs/AlSb superlattice photodiodes grown on a GaSb substrate, for the extended short wavelength infrared range. Reducing the majority carrier concentration from 2 × 1016 cm−3 to 2 × 1015 cm−3 caused the carrier diffusion length, Ldiff, to increase from 1.4 µm to 2.4 µm, respectively. This, in turn, increased the front-side illuminated quantum efficiency, without anti reflecting coating, at 300 K, λ = 2.18 µm and −0.1 V from 19% to 38%. At 200 K the 50% cutoff wavelength was 2.45 µm, the dark current density at −0.1 V was 2.4 × 10−5 A/cm2 and the detectivity was 2 × 1011 cm-Hz1/2/W. Using a gating technique on the mesa sidewall surface enabled the reduction of the dark current density.

The performance of focal plane arrays type-II InAs/GaSb superlattices (T2SL) based photo-detectors is limited by their operability (percentage of working pixels). Using preferential chemical etching we formed pits around “killer” defects found in InAs/GaSb T2SL epi-layers grown by MBE on GaSb (100). These pits were then studied with various microscopically methods, including optical, high resolution scanning electron (HRSEM), high resolution transmission electron (HRTEM), and cross-section scanning tunneling (XSTM) microscopies. We have found that these “killer” defects are related to both growth conditions and substrate imperfections. Adjusting these parameters allowed us to reduce “killer” defects density by several orders of magnitude. HRTEM inspection of the defects shows that at high growth temperatures they originate close to the T2SL–GaSb interface, and develop in size during only few SL loops to a straight and narrow “column” through the whole structure. At low growth temperatures most of them are nucleated on stacking fault defects formed on irregularities in the substrate surface.

InAs/GaSb and InAs/InAsSb type II superlattices have been proposed as promising alternatives to HgCdTe for the photon-absorbing layer of an infrared detector. When combined with a barrier layer based on an InAs/AlSb superlattice or an AlSbAs alloy, respectively, they can be used to make diffusion-limited “barrier” detectors with very low dark currents. In this work we compare theoretical simulations with experimental bandgap and photoabsorption data for such superlattices, spanning from the mid to the long-wave infra-red (2.3–12 μm). The spectral response of detectors based on these materials is also simulated. The simulations are based on a version of the k · p model developed by one of the authors, which takes interface contributions and bandgap bowing into account. Our results provide a way of assessing the relative merits of InAs/GaSb and InAs/InAsSb superlattices as potential detector materials.

InSb is a III–V binary semiconductor material with a bandgap wavelength of 5.4 μm at 77 K, well matched to the 3–5 μm MWIR atmospheric transmission window. When configured as a Focal Plane Array (FPA) detector, InSb photodiodes offer a large quantum efficiency, combined with excellent uniformity and high pixel operability. As such, InSb arrays exhibit good scalability and are an excellent choice for large format FPAs at a reasonable cost. The dark current is caused by Generation–Recombination (G–R) centres in the diode depletion region, and this leads to a typical operating temperature of ∼80 K in detectors with a planar implanted p–n junction. Over the last 15 years SCD has developed and manufactured a number of different 2-dimensional planar FPA formats, with pitches in the range of 15–30 μm. In recent years a new epi-InSb technology has been developed at SCD, in which the G–R contribution to the dark current is reduced. This enables InSb detector operation at 95–100 K, with equivalent performance to standard InSb at 80 K. In addition, using a new patented XBnn device architecture in which the G–R current is totally suppressed, epitaxial InAsSb detectors have been developed with a bandgap wavelength of 4.2 μm, which can operate in the 150–170 K range. In this short review of the past two decades, a number of key achievements in SCD’s InSb based detector development program are described. These include High Operating Temperature (HOT) epi-InSb FPAs, large format megapixel FPAs with high functionality using a digital Read Out Integrated Circuit (ROIC), and ultra low Size, Weight and Power (SWaP) FPAs based on the HOT XBnn architecture.

SCD has developed a range of advanced infrared detectors based on III-V semiconductor heterostructures grown on GaSb. The XBn/XBp family of barrier detectors enables diffusion limited dark currents, comparable with MCT Rule-07, and high quantum efficiencies. This work describes some of the technical challenges that were overcome, and the ultimate performance that was finally achieved, for SCD’s new 15 μm pitch “Pelican-D LW” type II superlattice (T2SL) XBp array detector. This detector is the first of SCD's line of high performance two dimensional arrays working in the LWIR spectral range, and was designed with a ~9.3 micron cut-off wavelength and a format of 640 x 512 pixels. It contains InAs/GaSb and InAs/AlSb T2SLs, engineered using k • p modeling of the energy bands and photo-response. The wafers are grown by molecular beam epitaxy and are fabricated into Focal Plane Array (FPA) detectors using standard FPA processes, including wet and dry etching, indium bump hybridization, under-fill, and back-side polishing. The FPA has a quantum efficiency of nearly 50%, and operates at 77 K and F/2.7 with background limited performance. The pixel operability of the FPA is above 99% and it exhibits a stable residual non uniformity (RNU) of better than 0.04% of the dynamic range. The FPA uses a new digital read-out integrated circuit (ROIC), and the complete detector closely follows the interfaces of SCD’s MWIR Pelican-D detector. The Pelican- D LW detector is now in the final stages of qualification and transfer to production, with first prototypes already integrated into new electro-optical systems.

XBnn mid-wave infrared (MWIR) detector arrays aimed at high operating temperature (HOT) applications, also known as barrier detectors or “bariodes”, are based on device elements with an InAsSb/AlSbAs heterostructure. There is no depletion layer in the narrow bandgap active layer of such devices, suppressing the usual Generation-Recombination (G-R) and Trap Assisted Tunneling (TAT) mechanisms for dark current that exist in standard narrow bandgap diodes. This yields lower dark currents in bariodes than in diodes with the same bandgap wavelength. InAsSb-bariode detectors, grown on lattice matched GaSb substrates have been shown previously to exhibit low dark current densities of ∼10-7 A/cm2 at 150 K. In this communication we show crystallographic and electro-optical characteristics of bariode structures grown on GaAs. Although the 7.8% mismatch causes a high density of dislocations, the devices still demonstrate electr-optical performance comparable with equivalent structures grown on GaSb, both for test devices and for focal plane array detectors (FPAs) with a 640×512 pixel format and a 15 μm pitch. This is in contrast to the behavior reported for InAsSb pin photodiodes grown on lattice mismatched substrates. The large leakage currents seen in the latter and attributed to a TAT mechanism, do not occur in the InAsSb-based bariodes grown on GaAs.

Oxide removal processes for InSb(100) and GaSb(100) substrates utilizing exposure to molecular hydrogen at moderate temperatures were studied in an experimental UHV chamber and were compared to the common method of thermal oxide desorption (TOD). Molecular hydrogen cleaning (MHC) deoxidizes the substrate surfaces effectively at temperatures of ∼100 and ∼200°C lower than that in TOD of GaSb and InSb, respectively. Closely related hydrogen based procedures for the cleaning of these materials before molecular beam epitaxial growth were developed. In these procedures a very low flux of atomic hydrogen was used in order to achieve short, yet mild, deoxidation of the substrates both with and without an Sb flux. These mild atomic hydrogen cleaning (MAHC) methods give smoother, cleaner, and more perfect InSb and GaSb surfaces after a shorter cleaning cycle at temperatures of 100–200°C lower than that in TOD. An Sb flux is not necessary in MAHC, but if used it gives a smoother substrate surface, and a well ordered...

When incorporated into the active layer of a "XBp" detector structure, Type II InAs/GaSb superlattices (T2SLs) offer a high quantum efficiency (QE) and a low diffusion limited dark current, close to MCT Rule 07. Using a simulation tool that was developed to predict the QE as a function of the T2SL period dimensions and active layer stack thickness, we have designed and fabricated a new focal plane array (FPA) T2SL XBp detector. The detector goes by the name of "Pelican-D LW", and has a format of 640 ×512 pixels with a pitch of 15 μm. The FPA has a QE of 50% (one pass), a cut-off of ~9.5 μm, and operates at 77K with a high operability, background limited performance and good stability. It uses a new digital read-out integrated circuit, and the integrated detector cooler assembly (IDCA) closely follows the configuration of SCD’s Pelican-D MWIR detector.

We report high performance long wavelength Zn doped p-type QWIPs grown by MOVPE. The p-QWIP detectors were tested under normal incident illumination. The detectors demonstrated high performance, in contrast to previous reports on Zn doped p-QWIP. At. 80 K, a bias of 2 V and a peak wavelength of 8.2 μm, a D* = 0.97 x 1010 cm Hz 0.5 /W was measured. The device exhibited a spectral electric field tunability of 2.7 μm. The photoluminescence spectra of the GaAs bulk and p-type GaAs well of the p-QWIP layer structure, were studied vs temperature and longitudinal electric field. The results of the photoluminescence spectra were correlated with the voltage tunability of the spectral response of the p-QWIP.

We fabricated and characterized InAs/AlSb Type II superlattice photodetectors for the short wave infrared region with λcutoff close to 2.5 μm. Using C-V and quantum efficiency measurements, we extracted the carrier diffusion lengths, Ldiff, and at 220 K and 300 K, they were 0.94 μm and 1.9 μm, respectively. In addition, I-V and detectivity measurements were carried out. The quantum efficiencies at λ = 2.18 μm, −50 mV, 300 K, and 200 K were 29% and 16% and the detectivities were above 1010 and 2 × 1011 cm Hz1/2/Watt, respectively. At a bias of −50 mV, the dark current densities at 300 K and 200 K were 4 mA/cm2 and 2.3 × 10−6 A/cm2 and the resistance-areas were 16 Ω cm2 and 38 kΩ cm2, respectively.

InAs/GaSb Type II superlattices (T2SLs) are a promising III-V alternative to HgCdTe (MCT) for infrared Focal Plane Array (FPA) detectors. Over the past few years SCD has developed the modeling, growth, processing and characterization of high performance InAs/GaSb T2SL detector structures suitable for FPA fabrication. Our LWIR structures are based on an XBpp design, analogous to the XBnn design that lead to the recent launch of SCD’s InAsSb HOT MWIR detector (TOP= 150 K). The T2SL XBpp structures have a cut-off wavelength between 9.0 and 10.0 μm and are diffusion limited with a dark current at 78K that is within one order of magnitude of the MCT Rule 07 value. We demonstrate 30 μm pitch 5 × 5 test arrays with 100% operability and with a dark current activation energy that closely matches the bandgap energy measured by photoluminescence at 10 K. From the dependence of the dark current and photocurrent on mesa size we are able to determine the lateral diffusion length and quantum efficiency (QE). The QE agrees very well with the value predicted by our recently developed k · p model [Livneh et al, Phys. Rev. B86, 235311 (2012)]. The model includes a number of innovations that provide a faithful match between measured and predicted InAs/GaSb T2SL bandgaps from MWIR to LWIR, and which also allow us to treat other potential candidate systems such as the gallium free InAs/InAsSb T2SL. We will present a critical comparison of InAs/InAsSb vs. InAs/GaSb T2SLs for LWIR FPA applications.

Over the past few years, a new type of High Operating Temperature (HOT) photon detector has been developed at SCD, which operates in the blue part of the MWIR atmospheric window (3.4 - 4.2 μm). This window is generally more transparent than the red part of the MWIR window (4.4 - 4.9 μm), and thus is especially useful for mid and long range applications. The detector has an InAsSb active layer and is based on the new "XBn" device concept, which eliminates Generation-Recombination dark current and enables operation at temperatures of 150K or higher, while maintaining excellent image quality. Such high operating temperatures reduce the cooling requirements of Focal Plane Array (FPA) detectors dramatically, and allow the use of a smaller closed-cycle Stirling cooler. As a result, the complete Integrated Detector Cooler Assembly (IDCA) has about 60% lower power consumption and a much longer lifetime compared with IDCAs based on standard InSb detectors and coolers operating at 77K. In this work we present a new large format IDCA designed for 150K operation. The 15 μm pitch 1280×1024 FPA is based on SCD's XBn technology and digital Hercules ROIC. The FPA is housed in a robust Dewar and is integrated with Ricor's K508N Stirling cryo-cooler. The IDCA has a weight of ~750 gram and its power consumption is ~ 5.5 W at a frame rate of 100Hz. The Mean Time to Failure (MTTF) of the IDCA is more than 20,000 hours, greatly facilitating 24/7 operation.

The impact of Te precipitates and impurities, in CdZnTe or CdTe substrates, on grown liquid phase epitaxy (LPE) HgCdTe layer hole concentrations was studied. The carrier concentrations in capped annealed LPE HgCdTe layers grown on CdZnTe substrates with large densities of Te precipitates are frequently significantly higher than those expected for HgCdTe annealed under Hg-deficient conditions. The carrier concentration in the LPE layer, due to the diffusion of copper ions from contaminated CdTe substrates into the layer, is strongly affected by the polarity of the (111)-oriented substrates. Layers grown on the (111)A face showed very high concentrations of Cu, whereas in those grown on the (111)B face normal carrier concentrations were achieved. These phenomena are discussed on the basis of defects formed either in the epilayer or in the layer-substrate interface.

Over the past few years, a new type of High Operating Temperature (HOT) photon detector has been developed at SCD, which operates in the blue part of the MWIR window of the atmosphere (3.4-4.2 μm). This window is generally more transparent than the red part of the MWIR window (4.4-4.9 μm), especially for mid and long range applications. The detector has an InAsSb active layer, and is based on the new "XBn" device concept. We have analyzed various electrooptical systems at different atmospheric temperatures, based on XBn-InAsSb operating at 150K and epi-InSb at 95K, respectively, and find that the typical recognition ranges of both detector technologies are similar. Therefore, for very many applications there is no disadvantage to using XBn-InAsSb instead of InSb. On the other hand XBn technology confers many advantages, particularly in low Size, Weight and Power (SWaP) and in the high reliability of the cooler and Integrated Detector Cooler Assembly (IDCA). In this work we present a new IDCA, designed for 150K operation. The 15 μm pitch 640×512 digital FPA is housed in a robust, light-weight, miniaturised Dewar, attached to Ricor's K562S Stirling cycle cooler. The complete IDCA has a diameter of 28 mm, length of 80 mm and weight of < 300 gm. The total IDCA power consumption is ~ 3W at a 60Hz frame rate, including an external miniature proximity card attached to the outside of the Dewar. We describe some of the key performance parameters of the new detector, including its NETD, RNU and operability, pixel cross-talk, and early stage yield results from our production line.

Crystal growth by the travelling heater method (THM) is considered to be a large scale, continuous, liquid phase epitaxial (LPE) process [e.g. R. Triboulet et al. J. Crystal Growth 79 (1986) 695]. We studied the structural perfection of Hg 1-x Cd x Te crystals grown by THM using preferential chemical etching and X-ray double crystal rocking curves. In principle, THM is similar to LPE; in practice, the Hg 1-x Cd x Te crystals are not epitaxially grown. The high temperature gradients involved in the THM growth process cause a stress field. This stress creates dislocations, which pile up by polygonization to form a veining pattern of low angle sub-grain boundaries (LASGBs) in the crystal. Such crystals, consisting of a mosaic of small, almost perfectly aligned single crystals, may only be considered oriented grown. The LASGBs have a major detrimental effect on the performance of photodiode arrays for the detection of infrared radiation. Diode leakage depends on the etch-pit density along the LASGB, the proximity of the diode and the extent of intersection of the diode by the LASGBs.

We have fitted the $\mathbf{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbf{p}$ model derived recently by one of the authors [Klipstein, Phys. Rev. B 81, 235314 (2010)] to experimentally measured photoabsorption spectra at 77 and 300 K for representative InAs/GaSb superlattices with band-gap wavelengths between 4.3 and 10.5 $\ensuremath{\mu}\mathrm{m}$. The model is able to reproduce the main features of the absorption spectra, including a strong peak from the zone boundary ${\mathrm{HH}}_{2}\ensuremath{\rightarrow}{E}_{1}$ transition. We have also used the same model to predict the band-gap wavelengths of over 30 more superlattices, measured by photoluminescence spectroscopy. The maximum error is 0.6 $\ensuremath{\mu}\mathrm{m}$, which corresponds to an uncertainty of less than 0.4 ML in layer width. This is comparable with the experimental uncertainty in layer widths, determined by in situ beam-flux measurements in the growth reactor. By eliminating all terms from the Hamiltonian, the energy contribution of which is less than the error due to the uncertainty in layer widths, the number of unknown fitting parameters has been reduced to six: two Luttinger parameters, three interface parameters, and the valence band offset. The remaining four Luttinger parameters are not independent and are determined from the two independent ones. Our set of Luttinger parameters is close to that reported by Lawaetz [Phys. Rev. B 4, 3460 (1971)], with a maximum deviation in any parameter of 0.6. The interface parameters are diagonal and have values of ${D}_{S}=3\phantom{\rule{0.28em}{0ex}}\mathrm{eV}\phantom{\rule{0.16em}{0ex}}\AA{}$, ${D}_{X}=1.3\phantom{\rule{0.28em}{0ex}}\mathrm{eV}\phantom{\rule{0.16em}{0ex}}\AA{}$, and ${D}_{Z}=1.1\phantom{\rule{0.28em}{0ex}}\mathrm{eV}\phantom{\rule{0.16em}{0ex}}\AA{}$ at 77 K. The off-diagonal interface parameters $\ensuremath{\alpha}$ and $\ensuremath{\beta}$ are too small to be fitted with any accuracy and have negligible effect on the unpolarized photoabsorption spectra. We also propose values for the room-temperature Luttinger and interface parameters. The fitted unstrained InAs/GaSb band overlap is 0.142 eV.

A bariode is a new type of "diode-like" semiconductor photonic device, in which the transport of majority carriers is blocked by a barrier in the depletion layer, while minority carriers, created thermally or by the absorption of light, are allowed to pass freely across the device. In an n-type bariode, also known as an XBnn structure, both the active photon absorbing layer and the barrier layer are doped with electron donors, while in a p-type bariode, or XBpp structure, they are both doped with electron acceptors. An important advantage of bariode devices is that their dark current is essentially diffusion limited, so that high detector operating temperatures can be achieved. In this paper we report on MWIR n-type bariode detectors with an InAsSb active layer and an AlSbAs barrier layer, grown on either GaSb or GaAs substrates. For both substrate types, the bariodes exhibit a bandgap wavelength of ~ 4.1 μm and operate with Background Limited Performance (BLIP) up to at least 160K at F/3. Different members of the XBnn device family are investigated, in which the contact layer material, "X", is changed between n-InAsSb and p-GaSb. In all cases, the electro-optical properties of the devices are similar, showing clearly the generic nature of the bariode device architecture. Focal Plane Array detectors have been made with a pitch of 15 or 30μm. We present radiometric performance data and images from our Blue Fairy (320×256) and Pelican (640×512) detectors, operating at temperatures up to 180K. We demonstrate for both GaSb and GaAs substrates that detector performance can be achieved which is close to "Rule 07", the benchmark for high quality, diffusion limited, Mercury Cadmium Telluride (MCT) devices.

The XBnn high operating temperature (HOT) detector project at SCD is aimed at developing a HOT (~150K) mid-wave infrared (MWIR) detector array, based on InAsSb/AlSbAs barrier detector or "bariode" device elements. The essential principle of the XBnn bariode architecture is to suppress the Generation-Recombination contribution to the dark current by ensuring that the depletion region of the device is contained inside a large bandgap n-type barrier layer (BL) and excluded from the narrow bandgap n-type active layer (AL). The band profile of the XBnn device leads to effective blocking of electron transport across the BL while maintaining a free path for the holes, thus assuring a high internal quantum efficiency (QE). Our devices exhibit a very large minority carrier lifetime (~700 ns), leading to a very low dark current of 50% of maximum response is ~ 4.1 μm. We show an image registered at 150K with a 640×512/15 μm Pelican FPA, using f/3.2 optics. The operability at 150K is >99.5% and the measured NETD, limited only by shot and Read-Out noise, is 20 mK for a 22 ms integration time. At this f/number, the detector has a background limited performance (BLIP) up to ~165K.

Hg1−xCdxTe crystals with x∼0.2 were grown by the traveling heater method (THM) in either the [111]A or the 1185 [111]B directions using oriented CdTe seeds. Lamellar and double position twins are sometimes formed during the growth of these crystals. The lamellar twinning occurs during the layer-by-layer mode of growth, and is due to high stresses originating from high thermal gradients. Double-position (DP) twins develop under multinucleated growth. This type of growth occurs towards the end of the growth run due to the concave shape of the growth interface at that stage. In crystals grown in the [111]A direction, the lamellar twins, of orientation [511]B, are constantly growing at the expense of the original [111]A oriented grain. Growth in the [111]B direction, on the other hand, suppresses the growth of the lamellar twin domain. The annihilation is due to arrays of small size interstitial Aδ+ ions. Ingots grown in the [111]B direction are almost entirely single crystalline, with a growth axis of the type. Photodiodes and capacitors realized on the (111)A plane are markedly superior to those on the lamellar twin plane, (511)B. The difference is due to a much higher fixed charge and larger fast surface state density in the case of the (511)B plane. These effects are explained by the lattice structures in the {111} and {511} planes and their possible influence on surface reactivity.

Fluoridic films produced by the anodization of Hg 1−x Cd x Te (x∼0.22) surfaces in nonaqueous solutions were characterized by Auger electron spectroscopy, x-ray photoelectron spectroscopy, and electron microprobe analysis. The films consist of three distinct regions. A thick uniform region, containing the fluorides of cadmium, mercury, and tellurium, and HgTe, is covered by a thin CdF 2 layer. The third region ― the film-substrate interface ― poor in mercury, consists mainly of CdF 2 and TeF 4

An XBn photovoltaic device has a band profile similar to that of a standard homojunction p-n diode, except that the depletion region is made from a wide bandgap barrier material with a negligible valence band offset but a large conduction band offset. In this notation, "X" stands for the n- or p-type contact layer, "B", for the n-type, wide bandgap, barrier layer, and "n", for the n-type, narrow bandgap, active layer. In this work, we report on the fabrication of XBn devices, which were grown by Molecular Beam Epitaxy (MBE) on GaSb substrates. Each structure has an InAsSb active layer of thickness ~1.5μm and a 0.2-0.5μm thick AlSbAs barrier layer. Good growth uniformity was achieved with lattice matching of better than 500ppm. Selected layers have been processed into devices which operate with a high internal quantum efficiency at a bias of ~0.1-0.2V, and which exhibit a very low dark current due to the strong suppression of the current component due to bulk Generation-Recombination processes. From dark current measurements, a minority carrier lifetime of >670nS has been estimated in devices with an active layer doping of ~4×1015cm-3. In optimized, lattice matched, devices with this doping and an active layer thickness of 4μm, a cut-off wavelength of ~ 4.0 - 4.1μm is expected at 160K, with a dark current density of ~10-6 A cm-2 and a quantum efficiency of >70% (λ

The chemical effects of annealing two cases of three-phase structures: ZnS-anodic-oxide-Hg1−xCdxTe and ZnS-anodic-fluoride-Hg1−xCdxTe used in infrared detector devices was studied using Auger electron spectroscopy. The presence of the three-element stable ion TeO32− in the HgCdTeO system and the absence of an analog three-element ion in the HgCdTeF system lead to completely different degradation mechanisms in the two structures studied. While the anodic oxide reacts readily with the underlying semiconductor, forming CdTeO3, the anodic fluoride is relatively stable in contact with the Hg1 −xCdxTe. On the other hand, the anodic fluoride reacts with the ZnS overlayer forming the stable ZnF2 and ZnTeO3 compounds and Te or HgTe. Electrical devices fabricated on Hg1 −xCdxTe using the two-layer ZnS-anodic-fluoride passivation process have a higher thermal stability than devices with the anodic oxide since the strong chemical interaction occurs at the ZnS-anodic-fluoride rather than at the critical fluoride-Hg1 −xCdxTe interface.

Detectors composed of novel Antimonide Based Compound Semiconductor (ABCS) materials offer some unique advantages. InAs/GaSb type II superlattices (T2SL) offer low dark currents and allow full bandgap tunability from the MWIR to the VLWIR. InAs1-xSbx alloys (x~0.1) also offer low dark currents and can be used to make MWIR devices with a cut-off wavelength close to 4.2μm. Both can be grown on commercially available GaSb substrates and both can be combined with lattice matched GaAlSbAs barrier layers to make a new type of High Operating Temperature (HOT) detector, known as an XBn detector. In an XBn detector the Generation-Recombination (G-R) contribution to the dark current can be suppressed, giving a lower net dark current, or allowing the same dark current to be reached at a higher temperature than in a conventional photodiode. The ABCS program at SCD began several years ago with the development of an epi-InSb detector whose dark current is about 15 times lower than in standard implanted devices. This detector is now entering production. More recently we have begun developing infrared detectors based both on T2SL and InAsSb alloy materials. Our conventional photodiodes made from T2SL materials with a cut-off wavelength in the region of 4.6μm exhibit dark currents consistent with a BLIP temperature of ~ 120-130K at f/3. Characterization results of the T2SL materials and diodes are presented. We have also initiated a program to validate the XBn concept and to develop high operating temperature InAsSb XBn detectors. The crystallographic, electrical and optical properties of the XBn materials and devices are discussed. We demonstrate a BLIP temperature of ~ 150K at f/3.

The study of HgCdTe technology in Israel began in the mid 1970's under the leadership of the late Prof. Kidron and his group at the Technion, Israel Institute of Technology. The R&D efforts were continued by other groups at the Technion and other universities and research institutes in Israel, as well as by SCD. Many aspects of the technology of this material were studied, including both bulk crystal and epitaxial growths and microelectronic fabrication methods, with an emphasis on surface treatment and passivation. Various characterization methods were developed to study both the basic and applied material and device properties. The efforts, reviewed in this article, matured at SCD as it commercialized the HgCdTe technology, launching large-volume production lines of state-of-the-art linear and multi-linear TDI LWIR detector arrays of various sizes from 10×1 to 480×6 elements. Over the years, SCD has supplied its customers with thousands of both photoconductive (PC) and photovoltaic (PV) detectors, which are briefly presented in the paper.

The chemical effects of annealing a three‐phase structure: ZnS–anodic fluoride–Hg1−xCdxTe used in infrared detector devices were studied using Auger electron spectroscopy (AES). The ZnS cap prevents the oxidation of the anodic fluoride upon annealing. The anodic fluoride is unstable in contact with the ZnS and a reaction takes place at their interface forming the stable ZnF2 compound and Te or HgTe. Nevertheless, the annealing does not affect the film–substrate interface as long as the fluoride has not reacted completely. This explains the relative thermal stability of electrical devices fabricated using this passivation scheme.

Fluoridic films produced by the anodization of Hg 1−x Cd x Te (x∼0.22) surfaces in nonaqueous solutions were characterized by Auger electron spectroscopy, x-ray photoelectron spectroscopy, and electron microprobe analysis. The films consist of three distinct regions. A thick uniform region, containing the fluorides of cadmium, mercury, and tellurium, and HgTe, is covered by a thin CdF 2 layer. The third region ― the film-substrate interface ― poor in mercury, consists mainly of CdF 2 and TeF 4

A technique which shows promise for achieving stable contacts is reported. This technique involves the selective oxidation of Ga in H2O/H2 mixtures simultaneous with the reaction of the metal and As to form a metal arsenide compound. The oxidation step is followed by removing the Ga2O3 layer using an acid etch. The large free energy of formation of gallium oxide enables the adjustment of the partial pressure of H2O to H2 so that only gallium is oxidized, while the GaAs substrate, metal, and metal arsenide are not. This method is discussed for three metal contacts to GaAs: In, Pt, and Cr. The technique was applied to GaPt/PtAs2/GaAs structures. The GaPt phase can be oxidized completely, whereas the inner PtAs2 is left unoxidized. The oxide can be etched off to leave a structure consisting only of platinum‐arsenide on the GaAs substrate.

Epitaxial layers of Hg1−xZnxTe(0.12≤x≤0.25) were grown by horizontal liquid phase epitaxy technique on closely lattice matched CdZnTe substrates. The growth conditions in which the rate of growth was limited by the diffusion of the solutes in the liquid were found. Post‐growth annealing study of the epilayers revealed the ability to control the epilayers electrical properties by in‐diffusion of Hg. The annealing at the temperature of 340 °C resulted in p‐type epilayers with hole concentration of ≊1×1016 cm−3 , mobility of 380–600 cm2 /V s and lifetime of 20–40 ns (for long‐wavelength infrared epilayers), measured at 77 K. The results of the annealing at the temperature of 220 °C were dependent on the annealing time and the substrates. n‐Type epilayers were characterized, showing electron mobility dependence on the energy band gap and temperature. The results of preliminary experiments of ion implantation into the annealed, p‐type epilayers are discussed.

Over the past few years SCD has developed a new InAlSb diode technology based on Antimonide Based Compound Semiconductors (ABCS). In addition SCD has lead in the development of a new standard of silicon readout circuits based on digital processing. These are known as the "Sebastian" family of focal plane processors and are available in 384 × 480 and 512 × 640 formats. The combination of ABCS diode technology with digital readout capability highlights an important cornerstone of SCDs 3rd generation detector program. ABCS diode technology offers lower dark currents or higher operating temperatures in the 100K region while digital readouts provide very low noise and high immunity to external interference, combined with very high functionality. In this paper we present the current status of our ABCS-digital product development, in which the detectors are designed to provide improved performance characteristics for applications such as hand-held thermal imagers, missile seekers, airborne missile warning systems, long-range target identification and reconnaissance, etc. The most important Detector-Dewar-Cooler Assembly (DDCA) parameters are reviewed, according to each specific application. Benefits of these products include lower power consumption, lighter weight, higher signal-to-noise ratio, improved cooler reliability, faster mission readiness, longer mission times and more compact solutions for volume-critical applications. All these advantages are being offered without sacrificing the standard qualities of SCDs InSb Focal Plane Arrays (FPAs), such as excellent radiometric performance, image uniformity, high operability and soft-defect cosmetics.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Antimonide Based Compound Semiconductors (ABCS) and a new family of advanced analogue and digital silicon read-out integrated circuits form the basis of the SCD 3rd generation detector program, which builds on the firm platform of SCDs existing InSb-FPA technology. We have devised a staged roadmap at SCD which begins with epitaxial InSb mesa diodes and gradually increases in technological sophistication. In the initial stages we have focused in particular on In 1-z Al z Sb alloys grown on InSb by Molecular Beam Epitaxy (MBE). Some of our achievements with these materials are presented in this paper. For epitaxial InSb (z = 0), we demonstrate the performance of Focal Plane Arrays (FPAs) with a format of 320x256 pixels, at focal plane temperatures between 77K and 110K. An operability has been achieved which is in excess of 99.5%, with a Residual Non-Uniformity (RNU) at 95K of less than 0.03% (standard deviation/dynamic range) between 15 and 80% well fill. Moreover, after a two point Non-Uniformity Correction (NUC) has been applied at 95K, the RNU remains below ~0.1% at all focal plane temperatures down to 85K and up to 100K without the need to apply any further correction. This is a major improvement in both the temperature of operation and the temperature stability compared with implanted diodes made from bulk material. We also demonstrate rapid progress in the development of epitaxial InAlSb FPAs with comparable operability and RNU to the InSb FPAs but which exhibit lower dark current and offer a range of cut-off wavelengths shorter than in InSb. These FPAs are intended for temperatures of operation in excess of 100K.

Antimonide Based Compound Semiconductors (ABCS) and a new family of advanced analogue and digital silicon read-out integrated circuits form the basis of the SCD 3rd generation detector program, which builds on the firm platform of SCDs existing InSb-FPA technology. In order to cover the MWIR atmospheric window, we recently proposed the epitaxial alloys: InAs1-y Sby on GaSb with 0.07 < y < 0.11 and In1-zAlz Sb on InSb with 0 < z < 0.03. In this paper we focus on the results of some of our recent work on epitaxial In1-zAlz Sb grown on InSb by Molecular Beam Epitxay (MBE). In epitaxial InSb (z = 0), we demonstrate the performance of Focal Plane Arrays (FPAs) with a format of 320x256 pixels, at focal plane temperatures between 77K and 100K. An operability has been achieved which is in excess of 99.5%, with a Residual Non-Uniformity (RNU) at 95K of less than 0.03% (standard deviation/dynamic range). Moreover, after a two point Non-Uniformity Correction (NUC) has been applied at 95K, the RNU remains below ~0.1% at all focal plane temperatures down to 85K and up to 100K without the need to apply any further correction. This is a major improvement in both the temperature of operation and the temperature stability compared with implanted diodes made from bulk material. We also demonstrate rapid progress in the development of low current epitaxial InAlSb photodiodes with high uniformity and low dark current that offer a range of cut-off wavelengths shorter than in InSb. Preliminary results are presented on FPAs with a cut-off wavelength in the range λC~5μ.

We propose that the antimonide family of semiconductors should be considered in some cases as a serious alternative to Mercury Cadmium Telluride (MCT) for the active region of next generation IR detectors, based on epitaxial materials. Among the alloys, epitaxial InAs1-ySby on GaSb with 0.07 < y < 0.11 and In1-zAlzSb on InSb with 0 < z < 0.03 together span important regions of the MWIR atmospheric window, yet exhibit strains of less than 0.15%. Both InSb and GaSb are binary substrates available in high quality. The sensitivity of bandgap to composition in In1-zAlzSb is similar to that in MCT. However, in InAs1-ySby this sensitivity is more than halved. In growth from the gas phase, the constraints on temperature stability are about 3 - 5 times lower than in MCT. Together, these characteristics make it easier to achieve high uniformity, particularly in InAs1-ySby. Finally, high quality superlattices based on InAs/Ga1-xInxSb can be grown by lattice matching to GaSb. This epitaxial material is emerging as an attractive alternative to MCT with a high degree of spatial uniformity and with an ability to span cut-off wavelengths from 3-20m in a single material system.

The oxidation of prereacted Pt films on (100) oriented n‐GaAs substrates was studied in the temperature range between 550 and 750 °C using Auger electron spectroscopy and Xe+ ion profiling. The GaPt/PtAs2/GaAs structure formed during annealing in hydrogen was oxidized using a mixture of water vapor and hydrogen. The GaPt phase can be oxidized completely, whereas the inner PtAs2 and GaAs interfaces are left unoxidized. The oxidation of the platinum‐gallium phase is self‐limited by the diffusion of the Ga through the gallium oxide overlayer. The oxide can be etched off to leave a structure consisting only of platinum‐arsenide on the GaAs substrate.

The transition to second generation backside-illuminated dense LWIR FPAs requires consideration of issues not previously relevant in first generation modules: unlike in front illuminated arrays, the MTF (or effective area) of a pixel is no longer close to the ideal sinc function. The cutoff wavelength, quantum efficiency and crosstalk depend on the thickness and composition grading of the epitaxial layer. The tradeoff between resolution and sensitivity demands extensive engineering and optimization of the array configuration. The transition was accomplished by comparisons of simulations with experimental results. Expectations of performance indicators, such as MTF, quantum efficiency and crosstalk were obtained by detailed Monte-Carlo simulations. The results were used to configure the focal plane array. This paper discuses the basic assumptions and simulation results and compares them with the performance of actual detectors and various test structures.