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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.

The InAs/InSb/GaSb/AlSb family of III-V alloys and superlattice materials offer unique possibilities for band structure engineering, because they can be grown on GaSb or InSb substrates with high quality and satisfactory control of strain, doping and composition. The band profiles and oscillator strengths are also quite predictable, enabling full simulation of detector performance from a basic knowledge of layer and stack thicknesses. In conventional III-V p-n devices, Shockley-Read-Hall (SRH) traps generate a significant flow of thermal carriers in the device depletion region. At SCD, we have overcome this problem by developing XBn and XBp barrier device architectures that suppress these depletion currents, leading to higher operating temperatures or lower dark currents. Our first barrier detector product was launched in 2013 and operates at 150K. It uses a mid-wave infrared (MWIR) XBn device with an InAsSb absorber well matched to the most transparent of the atmospheric windows, at wavelengths between 3 and 4.2μm. However to span the full MWIR and to sense the long-wave infrared (LWIR) spectrum, we have investigated InAs/GaSb type II superlattices (T2SLs), because they offer full tunability. In this work we show that minority carriers in n-type T2SLs are localized and diffuse by variable range hopping, even when the period is short and the valence miniband has a width of 30-40 meV. Unfortunately, this leads to sub-micron diffusion lengths and a low quantum efficiency (QE) of ~20% in a full MWIR XBn device. On the other hand, p-type layers exhibit “metallic” minority carrier transport with much longer diffusion lengths, typically ~7 μm in our LWIR device layers. The successful development of p-type devices has led to our second barrier detector product, which uses an XBp LWIR T2SL and operates at 77K with a cut-off wavelength of 9.5 μm, a focal plane array (FPA) QE of ~50% and background limited performance up to ~90K at F/3. Moreover, the FPA operability is typically above 99.5%, based on stringent production-line criteria. Together with high spatial uniformity and good temporal stability, these barrier detectors are already a realistic alternative to MCT photodiode arrays, and further products operating at other wavelengths will be launched in due course.

SCD introduced its first cooled two-dimensional (2D) Mid-Wave Infrared (MWIR) detector more than twenty years ago. The InSb Focal Plane Array (FPA) had a 30 μm pitch and approximately 80,000 pixels. We have since introduced 2D MWIR detectors with pitches of 25, 20, 15 and 10 μm and an increasing number of pixels, up to 3 M-pixel. By decreasing the pixel size, it is possible to increase their overall number in a given die size, leading to a higher resolution and opening the way for new applications such as persistent surveillance. On the other hand, maintaining the same number of pixels leads to a much smaller die size, which enables detectors to be manufactured with a lower Size, Weight, Power and Cost (SWaP-C). Reducing the pixel dimensions can also reduce the size of the optics to support lower SWaP-C at the system level. The novel XBn-InAsSb technology enables High Operating Temperature (HOT) MWIR FPA, normally operated at 150K, for lower SWaP and longer lifetime cooler, detector and system. To date, HOT MWIR detectors of several formats, with 15 and 10 μm pitch, are integrated in numerous electro-optical systems for many defense and commercial applications. Achieving even smaller pixel size while maintaining the same electro-optical performance, namely high quantum efficiency, low dark current, low cross talk, and high array uniformity, is a serious technological challenge. In this work, we present SCD's new HOT MWIR detector (CRANE) with 2560×2048 format and 5μm pitch.

SCD has developed advanced technologies for small pitch, large format and high operating temperature detector arrays, based on III–V materials and novel barrier architectures. These detectors operate with background limited performance in the Long-, Mid- and Short-wave infrared, with high uniformity and good stability. In all cases the pixel operability is above 99.5%.

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

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.

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.

For the highest end mid-wave-infrared applications, SCD, France offers a family of cryogenically cooled detectors with background limited performance (BLIP). The matured InSb planar technology is implemented in a variety of focal plane arrays, from a 320 x 256 format with a 30 µm pitch to a 1280 x 1024 format with a 15 µm pitch, all of which are operated at 77K. A major challenge is to reduce the cooling requirements. Then substantial reductions in size, weight, and power (SWaP) can be achieved by using a smaller cooler and Dewar assembly. SCD’s new epi-InSb detectors, grown by molecular beam epitaxy, have a BLIP temperature of ~100 K at F/3. This enhanced operating temperature reduces the required cooling power by ~20 % compared with the conventional 77 K operation. For a very high operating temperature, we have developed the new XBn-InAsSb detector with a 4.2 µm cut-off wavelength. This detector exhibits a BLIP temperature of ~160K at F/3 and a reduction in cooling power of ~60 %. These HOT detectors enable an improved range of solutions, including faster cool-down time and mission readiness, longer mission times, and higher cooler reliability. We can also exploit their reduced dark current to obtain an enhanced signal to noise ratio at lower operating temperatures. The well-established 25 µm pitch family of uncooled µ-Bolometer detectors has two basic formats, 384 x 288 and 640 x 480, and several sensitivity grades. The very high sensitivity 25 µm pitch detector has been demonstrated at F/2.4 for mid-range systems. The wide-band detector is optimized for both the long-wave-infrared and mid-waveinfrared spectral bands. Recently we developed the new 17 µm pitch family of detectors. The 640 x 480 format is a leading candidate for applications such as thermal weapon sights, driver vision enhancers and other mid-range IR systems. The 17 µm family is currently being expanded with the high sensitivity grade and with the addition of two new formats: the compact 384 x 288 for low SWaP applications, and the large 1024 x 768 format for applications requiring high resolution and a wide field of view.

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.

The growth, by MOVPE, of a range of antimonide-based material systems suitable for providing devices responsive to 2-4 mu m wavelength radiation is reported. Photodetectors with external quantum efficiencies of 60% at 2.2 mu m have been fabricated from an InGaSb homojunction. In order to examine the possibility of tuning the wavelength of emission or detection by using a strained single quantum well (SSQW) of InGaSb/GaSb this has been grown in the depletion region of a GaSb homojunction. These novel heterostructures have been grown to produce devices without the need for conventional doping. Using the crossed-gap alignment of InAs/GaSb the authors can form a diode-like structure. The most promising devices have a turn-on voltage VTO of 0.7 V (1mA), and a typical reverse voltage VR=-12 V (0.1 mA) and a best VR of -12 V (10 mu A) for a 100 mu m diameter device with some evidence of avalanche breakdown in the structure. Abrupt doping junctions have been formed between GaSb and GaAs:Si substrates. The mismatch between the layers is ameliorated by using a low-temperature buffer layer to improve the interface. Avalanche breakdown starts at -4.5 V in these structures and reverse bias currents of

Shrinking the pixel size in advanced infrared Focal Plane Array (FPA) detectors allows either a reduction in the system size for the same number of pixels, or an increase in the pixel count for the same focal plane area. Smaller pitch and increased pixel count enables new applications such as long range surveillance, advanced Search and Track, missile warning, persistent surveillance, and infrared spectroscopy. In the last two decades SCD has followed this path of reducing the pixel size in InSb detectors for Mid-Wave Infrared (MWIR) applications, developing and manufacturing FPAs from 30μm down to 10μm pitch. The Blackbird InSb detector with 1920×1536/10μm format was introduced in 2013. Modern electro-optical systems are also designed towards a more compact, low power, and lower cost solution compared with traditional systems. In order to meet these requirements, detectors are being developed to work at Higher Operating Temperatures (HOT). In the last few years SCD has introduced 15μm pitch MWIR detectors based on the novel XBn-InAsSb technology, which enables outstanding electro-optical performance at temperatures as high as 150K. Two XBn FPA formats were developed and are now in production: 640×512/15μm and 1280×1024/15μm. Following the above trends, SCD is currently developing a 10μm XBn pixel, designed to operate at 150K with performance similar to the mature 15μm pixel. In this paper we present results from XBn FPA test devices, where the XBn array is flip-chip bonded to a Readout Integrated Circuit (ROIC) with a 10μm pitch. Test measurements in a laboratory Dewar at 150K demonstrate dark currents of 250fA, quantum efficiency greater than 70%, pixel operability of higher than 99.5%, and excellent array uniformity.

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.

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.

The XBn/XBp family of barrier detectors enables diffusion limited dark currents comparable with HgxCd1-xTe Rule-07 and high quantum efficiencies. SCD’s XBp type II superlattice (T2SL) detector contains InAs/GaSb and InAs/AlSb T2SLs, and was designed for the long wave infrared (LWIR) atmospheric window using k · p based modeling of the energy bands and photo-response. 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 hybridisation, under-fill, and back-side polishing. The 640 × 512 pixel, 15 μm pitch, detector goes by the name of ‘Pelican-D LW’ and exhibits a quantum efficiency of ~ 50 per cent with background limited performance at an operating temperature of 77 K. It has a cut-off wave length of ~ 9.5 μm, with a pixel operability of above 99 per cent. The detector gives a very stable image with a residual non uniformity of below 0.04 per cent over its useful dynamic range. A new digital read-out integrated circuit has been designed so that the complete detector closely follows the configuration of SCD’s MWIR Pelican-D detector.

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 real and imaginary components of the GaAs refractive index at temperatures between 20-700 degrees C have been obtained. Measurements were made by comparing the variable angle reflectivity of p-polarized and s-polarized 633 nm wavelength light from a deoxidized GaAs surface. By using these temperature-dependent optical constants for GaAs, modeling has allowed the behavior of surface photoabsorption (SPA) signals with temperature and oxide layers present to be predicted for different angles of incidence. The experimentally observed SPA signals during deoxidization of GaAs show strong qualitative agreement with these calculations at each of the angles of incidence considered. The measurement of data and application to modeling provides a platform for the measurement of temperature-dependent optical data for other III-V materials and for the investigation of deoxidation mechanisms.

Surface photoabsorption (SPA) is an in situ technique for monitoring III–V semiconductors in an MOVPE reactor. When used in conjunction with UV absorption, it gives information about the strain associated with the growth of ideal (one monolayer) and nonideal (more than one monolayer) GaAs interfaces in InAs/GaSb superlattices. Raman scattering has been used as an ex situ technique for quantifying the strain in these superlattices. It is found that the LO frequency blue shifts by 3 cm −1 when nonideal interfaces are grown.

InAs/GaSb strained layer superlattices have been grown by atmospheric pressure MOVPE and the growth conditions optimised by observing, in real time, the in-situ UV absorption of the alkyls in the growth chamber. The Raman scattering of folded longitudinal acoustic phonons in the superlattices has been used as a probe of the periodicity of the superlattice. Atomic force microscopy has also been used to give information about the final surface morphology and RMS roughness of the superlattices. By combining all three techniques, optimum conditions have been found for the growth of short period InAs/GaSb superlattices. These have been used to sandwich a long period superlattice designed for transport measurements. The use of the short period superlattices eliminated additional conducting layers at each end of the semimetallic superlattice and produced structures where the hole and electron densities are equal. Such structures exhibit a dramatic new quantum transport effect where the Hall resistance goes to zero at high pressures and low temperatures.

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.

We present an alternative method for determining the shear deformation potential b of the valence band in III-V semiconductors. Instead of bulk semiconductors we use quantum well structures and apply uniaxial stress perpendicular to the growth direction. Using analytical solutions we show that the first confined hole state has a pronounced and characteristic nonlinear energy shift with respect to stress. This allows the hydrostatic and shear deformation potentials a and b to be determined independently from the stress dependence of the bandgap only, which can be measured by a wider range of experimental techniques than those necessary for obtaining deformation potentials from bulk material. Measurements on a (GaAs)10/(AIAs)10 superlattice yielded a value for b which is in good agreement with recent results from bulk measurements and hence support the validity of our proposed method.

InAs GaSb strained layer superlattices (SLSs) have been grown by metalorganic vapour phase epitaxy (MOVPE) at atmospheric pressure. Initially the interfaces of the SLS have been biased towards pairs of GaAs or InSb using three different gas switching sequences. Room temperature Raman optical modes show that growing the interfaces using an ALE (atomic layer epitaxy) like switching sequence gives interfaces of very high quality probably near the optimum, which is a monolayer, Growing with other switching sequences leads to one of the interfaces being non-uniform. By growing samples with alternating (InSb,GaAs or GaAs,InSb) pairs of interfaces it is possible to unambiguously assign this non-uniformity to one of the two possible interfaces for the first time. Furthermore, the influence of the band overlap on interface type has been studied using optimised SLSs in the semimetallic regime.

Short wavelength Infra Red (SWIR) imaging has gained considerable interest in recent years. The main applications among others are: active imaging and LADAR, enhanced vision systems, low light level imaging and security surveillance systems. In this paper we will describe SCD's considerable efforts in this spectral region, addressing several platforms: 1. Extension of the mature InSb MWIR product line operating at 80K (cut-off wavelength of 5.4mm). 2. Extension of our new XBnn InAsSb "bariode" technology operating at 150K (cut-off of 4.1mm). 3. Development of InGaAs detectors for room temperature operation (cut-off of 1.7mm) 4. Development of a SNIR ROIC with a low noise imaging mode and unique laser-pulse detection modes. In the first section we will present our latest achievements for the cooled detectors where the SWIR region is combined with MWIR response. Preliminary results for the NIR-VIS region are presented where advanced substrate removal techniques are implemented on flip-chip hybridized focal plane arrays. In the second part we will demonstrate our VGA, 15mm pitch, InGaAs arrays with dark current density below 1.5nA/cm2 at 280K. The InGaAs array is hybridized to the SNIR ROIC, thus offering the capability of low SWaP systems with laser-pulse detection modes.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

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.

InAs/GaSb strained layer superlattices (SLSs) have been grown by metalorganic vapour phase epitaxy (MOVPE) at atmospheric pressure. Whilst long period SLSs have been successfully grown by this technique, the growth of short period structures is adversely affected by step-bunching. By growing the SLSs faster and cooler, good periodicity was achieved as measured by Raman spectroscopy, transmission electron microscopy (TEM) and X-ray diffraction (XRD) in SLSs with bilayer (GaSb + InAs) thicknesses as thin as 50 A. We have also detected the InSb-like and GaAs-like interface modes from room temperature Raman measurements for the first time in MOVPE grown samples. The most promising samples have been assessed by FIR photoconductivity at 4.2 K and show bandgaps (dependent on the bilayer thickness) between 5 and 20 μm.

We have performed a Raman scattering study of GaSb/InAs superlattices grown by MOVPE using different gas switching sequences to control the interface type. The identification of an InSb interface mode, clearly resolved already at room temperature, has been revised. A strongly localised GaAs-like interface mode has been used for the first time to characterise sequentially grown interfaces in an independent and selective way.

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.

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

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.

A barrier photodetector is a device in which the light is absorbed in a narrow bandgap semiconductor layer whose bands remain essentially flat or accumulated at the operating bias so that all carrier depletion is excluded. In a conventional photodiode below a threshold temperature T0, typically 130-150K for MWIR devices, the dark current is due to Generation-Recombination (G-R) centres in the depletion layer. In a barrier detector, the absence of depletion in the narrow bandgap semiconductor ensures that the G-R contribution to the dark current is negligible. The dark current in the barrier detector is thus dominated by the diffusion component, both above and below T0. Therefore, at a given temperature below T0, a barrier detector will exhibit a lower dark current than a conventional photodiode with the same cut-off wavelength. Alternatively, for a given dark current, a barrier detector will operate at a higher temperature than a conventional photodiode, provided that this temperature is below T0. Device architectures are presented for barrier detectors with photon absorbing layers based on InAs1-xSbx alloys and type-II InAs/GaSb superlattices (T2SL). The thermionic and tunneling components of the dark current are analyzed and shown to be negligible for typical device parameters. An operating temperature of ~150K is estimated for a MWIR barrier detector with f/3 optics and a cut-off wavelength of 4.2μ.

This paper describes 17-K, electric-field-dependent electroreflectance and electrotransmission measurements on two GaAs/${\mathrm{Al}}_{0.3}$${\mathrm{Ga}}_{0.7}$As multiple-quantum-well (MQW) samples, grown by metalorganic vapor-phase epitaxy (MOVPE). Photocurrent and transmission spectra are also taken at different biases for comparison. It is shown how each of these four spectroscopies provide complementary information and how this allows clear deductions to be made about the microscopic structure of the MQW stack. In particular, each technique shows splittings of the E1H1 and E1L1 features, which it is argued derive from sudden changes in the well width at certain depths in the stack. Several measurements demonstrate that the region with wider wells lies deeper in the structure. Under flatband conditions, these monolayer splittings would be smaller than the optical linewidth of the individual quantum wells and would thus be unresolvable. However, the unintentional background doping of the MQW's results in the field being larger at the back of the stack than that at the front, and this enhances the splitting. Hence we have been able to observe monolayer splittings in wider wells (87 and 158 \AA{}) than previously reported. The size of the splittings for both samples, the relative height of the split features in the different spectroscopies, and their dependence on the applied bias are all in agreement with our model for the structure of the stack. The imperfections of the stack have important consequences for MOVPE-grown optoelectronic devices that incorporate MQW's.

In this study, we demonstrate how electroreflectance (ER) measurements as a function of bias, and of angle of incidence (θ0), together with bias dependent photocurrent (PC) measurements, can be used to provide understanding of the complex electric field profile and carrier transport effects in a GaAs/Al0.3Ga0.7As multiple quantum well (MQW), grown inside n+ contact layers. The PC measurements exhibit split excitonic features, the components of which change in strength with the applied bias. The effect is explained by absorption in the front of the MQW stack, with the back of the stack acting as detector. We examine the θ0-dependence of the ER lineshape, to determine the depth of the layers responsible for each feature. The ER and PC lineshapes and their bias dependence are explained by the unusual electric field profile across the stack. The field profile appears to be determined by tunnelling of the dark current.

We derive analytical formulae for the modulated reflectance lineshapes of both single (SQQ) and multiple (MQW) quantum well structures, by considering optical interference between the different reflected rays. The SQW lineshape is shown to be extremely sensitive to the optical phase delay between the rays reflected from the well and the front surface. Consequently, each well in a MQW makes a different contribution to the overall lineshape, depending upon its depth below the sample surface. This results in very complicated lineshapes for thick MQW stacks, whose form we discuss in detail. Calculations are made using typical parameters and comparisons are drawn with experimentally measured spectra.

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.

For over 27 years, SCD has been manufacturing and developing a wide range of high performance infrared detectors, designed to operate in either the mid-wave (MWIR) or the long-wave (LWIR) atmospheric windows. These detectors have been integrated successfully into many different types of system including missile seekers, time delay integration scanning systems, hand-held cameras, missile warning systems and many others. SCD’s technology for the MWIR wavelength range is based on its well established 2D arrays of InSb photodiodes. The arrays are flip-chip bonded to SCD’s analogue or digital signal processors, all of which have been designed in-house. The 2D focal plane array (FPA) detectors have a format of 320×256 elements for a 30-μm pitch and 480×384 or 640×512 elements for a 20-μm pitch. Typical operating temperatures are around 77–85 K. Five years ago SCD began to develop a new generation of MWIR detectors based on the epitaxial growth of antimonide based compound semiconductors (ABCS). This ABCS technology allows band-gap engineering of the detection material which enables higher operating temperatures and multi-spectral detection. This year SCD presented its first prototype FPA from this program, an InAlSb based detector operating at a temperature of 100 K. By the end of this year SCD will introduce the first prototype MWIR detector with a 640×512 element format and a pitch of 15 μm. For the LWIR wavelength range SCD manufactures both linear Hg1−xCdxTe (MCT) detectors with a line of 250 elements and time delay and integration (TDI) detectors with formats of 288×4 and 480×6. Recently, SCD has demonstrated its first prototype uncooled detector which is based on VOx technology and which has a format of 384×288 elements, a pitch of 25 μm, and a typical NETD of 50 mK at F/1. In this paper, we describe the present technologies and products of SCD and the future evolution of our detectors for the MWIR and LWIR detection.

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.

We demonstrate the suppression of the bulk generation- recombination current in nBn devices based on an InAsSb active layer (AL) and a AlSbAs barrier layer (BL). This leads to much lower dark cur- rents than in conventional InAsSb photodiodes operating at the same temperature. When the BL is p-type, very high doping must be used in the AL (nBpn + ). This results in a significant shortening of the device cut- off wavelength due to the Moss-Burstein effect. For an n-type BL, low AL doping can be used (nBnn), yielding a cutoff wavelength of ∼4.1 μm and a dark current close to ∼3 × 10 −7 A/cm 2 at 150 K. Such a device with a4 -μm-thick AL will exhibit a quantum efficiency (QE) of 70% and background-limited performance operation up to 160 K at f/3. We have madenBnnfocalplane arraydetectors(FPAs)with a 320 ×256 formatand a 1.3-μm-thick AL. These FPAs have a 35% QE and a noise equivalent temperature difference of 16 mK at 150 K and f/3. The high performance of our nBnn detectors is closely related to the high quality of the molecular beam epitaxy grown InAsSb AL material. On the basis of the temperature dependence of the diffusion limited dark current, we estimate a minority carrier lifetime of ∼670 ns. C 2011 Society of Photo-Optical Instrumentation Engineers

The core of SCD’s present day focal plane array (FPA) technology is a two-dimensional array of InSb photodiodes. It is produced by ion implantation and is attached to a silicon focal plane processor by indium bumps. We have extended this technology with In1−xAlxSb (0

We present the design of an electro-optic modulator which is based on the quantum-confined Stark effect (QCSE) in GaAs quantum wells contained within the central layer of a Fabry-Perot etalon. The etalon mirrors are quarter wave stacks of Ga0.7A10.3As and AlAs, eliminating the need for the application of anti-reflection coatings. p-i-n-doping is employed with the undoped Or stack sandwiched between doped mirrors, enabling electric fields of the order of 105Vcm-1 to be readily developed across the quantum wells. Placing a multiple quantum well structure within an etalon resonant cavity gives flexibility of design in terms of operating wavelength and mode: Light incident perpendicular to the QW stack is modulated through the operation of the QCSE on the QW excitons, either electro-refractively by a change in the real part of the QW refractive index producing a wavelength modulation of the narrow-band Fabry-Perot transmission resonance or in electro-absorptive mode. The semi-empirical theory uses conventional multilayer optical matrix methods together with a recent theory of the QCSE which has been tested against the results of electro-reflectance experiments. In electro-absorption mode we find a ratio of 19:1 on:off at 857.5nm for 8 quantum wells. In electro-refractive mode, using 32 wells, we predict modulation from 10% to 76% reflection at 883nm. These figures exclude substrate effects. Extension of the theory to other materials systems is readily accomplished. We present the reflectivity spectrum of a high quality etalon in In0.53Ga0.47As/InP and find good agreement with the predictions of the optical matrix model.

We have measured the current-voltage (I-V) of type II InAs/GaSb/InAs double heterojunctions (DHETs) with 'GaAs like' interface bonding and GaSb thickness between 0-1200 \AA. A negative differential resistance (NDR) is observed for all DHETs with GaSb thickness $>$ 60 \AA below which a dramatic change in the shape of the I-V and a marked hysteresis is observed. The temperature dependence of the I-V is found to be very strong below this critical GaSb thickness. The I-V characteristics of selected DHETs are also presented under hydrostatic pressures up to 11 kbar. Finally, a mid infra-red electroluminescence is observed at 1 bar with a threshold at the NDR valley bias. The band profile calculations presented in the analysis are markedly different to those given in the literature, and arise due to the positive charge that it is argued will build up in the GaSb layer under bias. We conclude that the dominant conduction mechanism in DHETs is most likely to arise out of an inelastic electron-heavy-hole interaction similar to that observed in single heterojunctions (SHETs) with 'GaAs like' interface bonding, and not out of resonant electron-light-hole tunnelling as proposed by Yu et al. A Zener tunnelling mechanism is shown to contribute to the background current beyond NDR., Comment: 8 pages 12 figs