Showing papers on "Mercury cadmium telluride published in 2004"

Third-generation focal plane array IR detection modules and applications

Abstract: The 3rd generation of infrared (IR) detection modules is expected to provide advanced features like higher resolution 1024x1024 or 1280x720 pixels and/or new functionalities like multicolor or multi band capability, higher frame rates and better thermal resolution. This paper is intended to present the current status at AIM on the Mercury Cadmium Telluride (MCT), quantum well (QWIP) and antimonide superlattices (SL) detection modules for ground and airborne applications in the high performance range. For high resolution a 1280x720 MCT device in the 3-5μm range (MWIR) is presently under development. For spectral selective detection, a QWIP detector combining MWIR and 8-10μm (LWIR) detection in each pixel has been developed in a 384x288x2 format with 40 μm pitch, NETD 12 mk @ F/2 and 5 ms. The next step will now be to stabilize the technology and to start the development of a dual color MWIR device based on SL technology and the existing 384 x 288 read out circuit (ROIC) used in the dual band QWIP device.

2Kx2K molecular beam epitaxy HgCdTe detectors for the James Webb Space Telescope NIRCam instrument

Abstract: The NIRCam instrument will fly ten of Rockwell Scientific’s infrared molecular beam epitaxy HgCdTe 2048x2048 element detector arrays, each the largest available with current technology, for a total of 40 Megapixels. The instrument will have two varieties of MBE HgCdTe, a SWIR detector with λco = 2.5 μm, for the shortwave channel of NIRCam (0.6-2.3 μm); and a MWIR detector with λco = 5.3 μm, for the longwave channel of NIRCam (2.4-5.0 μm). Demonstrated mean detector dark currents less than 0.01 electrons per second per pixel at operating temperatures below 42 K for the MWIR and below 80 K for the SWIR, combined with quantum efficiency in excess of 80 percent and read noise below 6 electrons rms, make these detector arrays by far the most sensitive SWIR and MWIR devices in the world today. The unique advantages of molecular beam epitaxy as well as FPA data on noise, dark current, quantum efficiency, and other performance metrics will be discussed. In addition, the focal plane assembly package designs will be presented and discussed.

Performance and application of a new planar array infrared spectrograph operating in the mid-infrared (2000-975 cm(-1)) fingerprint region.

Abstract: A no-moving-part planar array infrared spectrograph (PA-IR) equipped with a 256 × 256 mercury cadmium telluride (MCT) focal plane array has been designed and constructed. The performance of the instrument, whose frequency range extends from 2000–975 cm-1 , has been assessed in terms of resolution, bandwidth, and signal-to-noise ratio. The PA-IR spectrograph is able to record spectra with an 8.7 ms time resolution and has peak-to-peak noise levels as low as 2.4 × 10-4 A.U. As a demonstration of the potential of PA-IR, the dynamics of reorientation of a liquid crystalline sample exposed to a single electric field pulse has been studied. It was shown that PA-IR can be used for the simultaneous acquisition of two orthogonally polarized spectra. The advantages and limitations of PA-IR, step-scan Fourier transform infrared (FT-IR), and ultrarapid-scanning FT-IR for real-time studies of reversible and irreversible phenomena are thoroughly discussed.

Performance of large-format 2Kx2K MBE-grown HgCdTe Hawaii-2RG arrays for low-flux applications

Abstract: VLT instruments increasingly require high sensitivity large format focal planes. Adaptive optics combined with multiple integral field units feeding high resolution spectrographs drive the pixel performance as well as the array format. Three VLT instruments, the wide field imager Hawk-I and the integral field spectrographs SINFONI and KMOS will be equipped with MBE-grown HgCdTe Hawaii-2RG arrays, which have a cut-off wavelength of 2.5 micron. The Hawaii-2RG array was originally developed for the near infrared camera of JWST having a cut-off wavelength of 5 micron. The Hawaii-2RG multiplexer is one of the most advanced readout architectures offering a large variety of operating modes. A special 32 channel package has been developed which allows reading out all 32 output channels of the detector in parallel. Symmetric cryogenic CMOS operational amplifiers are placed next to the focal plane instead of using ASIC’s which are not yet available. The internal bus of the detector is accessed directly, bypassing the on-chip buffer amplifier. Noise performance employing different techniques of using reference pixels is discussed. Basic performance characteristics of the Hawaii-2RG arrays will be presented. Unlike LPE arrays, which lose quantum efficiency at lower temperatures, MBE arrays with λc = 2.5 μm do not show this effect. However, the MBE arrays under test still suffer from persistence.

Further characterization of Rockwell Scientific LWIR HgCdTe detector arrays

Abstract: Future infrared space missions will undoubtedly employ passively cooled focal plane arrays (T ~ 30K), as well as passively cooled telescopes Most long-wave detector arrays (eg Si:As IBC) require cooling to temperatures of ~ 6-8K We have been working with Rockwell Scientific Company to produce <= 10 micron cutoff HgCdTe detector arrays that, at temperatures of ~30K, exhibit sufficiently low dark current and sufficiently high detective quantum efficiency, as well as high uniformity in these parameters, to be interesting for astronomy Our goal is to achieve dark current below the target value of ~ 30 e-/s/pixel with at least 60mV of actual reverse bias across the diodes at T ~ 30K To this end, Rockwell Scientific Company has delivered three 10 micron cutoff HgCdTe low dark current detector arrays with small capacitance diodes for characterization in Rochester The most recent presentation showed the remarkable preliminary performance of the first of these devices We present further results on the first device along with results on the subsequent two deliveries

Sensitivity improvement in surface infrared spectroscopy: Design, characteristics, and application of a high-temperature graphite source

Abstract: An infrared source designed to increase the sensitivity of the technique of reflection absorption infrared spectroscopy (RAIRS) for the detection of molecular adsorbates at submonolayer coverages on metal surfaces is described. The source is based on a graphite element with a lifetime of 500 h when operated at a temperature of ∼2300 K in a static pressure of 800 Torr of argon. The design allows for rapid and easy replacement of the low cost graphite element. The signal-to-noise ratio (SNR) achieved with this source for spectra obtained with both mercury cadmium telluride and indium antimonide detectors is a factor of 3-higher than obtained with a standard silicon carbide (SiC) source operated at ∼1500 K. With the higher SNR available with the graphite source it was possible to detect two vibrational features, δs(CH3) of methyl at 1247 cm–1, and ν(CH) of methylidyne at 2956 cm–1, that were not detected in previous RAIRS studies.

Long-wavelength infrared focal plane arrays fabricated from HgCdTe grown on silicon substrates

Abstract: We have demonstrated the successful growth of mercury cadmium telluride (MCT) infrared detector material on silicon substrates. Growth on silicon increases the maximum achievable array size, reduces manufacturing costs, and paves the way for infrared detector growth directly on multiplexing circuits. In addition, the thermal match with multiplexing circuits eliminates the requirement for complex thinning procedures. Since the crystal lattice of MCT is not matched to that of silicon, an intermediate buffer layer is required. We have developed a buffer layer technique that is compatible with MCT grown by Metal Organic Vapour Phase Epitaxy (MOVPE). Long-wavelength heterostructure device designs were grown using this technique. Test devices and 128x128 focal plane arrays were fabricated by wet etching mesa structures and passivating the mesa side-walls with a thin layer of CdTe. An indium flip-chip technique was used to form interconnects between the detector material and test or multiplexing circuit. At 77K, 50x50μm test devices with a 10.2μm cut off wavelength have been measured with R0A~1x103Ohm cm2 at zero bias and R.A~1x104Ohm cm2 at 0.1V reverse bias. Arrays from this material have been demonstrated with operabilities up to 99.7%.

Low-cost PbSalt FPAs

Abstract: Current mid-wave infrared detector technologies, such as Indium Antimonide, Mercury Cadmium Telluride, and Platinum Silicide, require the use of expensive, heavy, and power hungry cryogenic coolers or expensive multistage thermoelectric coolers. There is a need for a low cost uncooled mid-wave infrared (MWIR) technology for use in applications where cost, power, size, and reliability are of most importance. Northrop Grumman Electro-Optical Systems (EOS) is currently developing such a sensor based upon its low cost Lead Selenide (PbSe) detector technology. Utilizing its extensive production experience in producing high performance linear PbSe arrays, EOS has developed a 320X256 staring PbSe Focal Plane Array. This paper provides a summary and status of the development efforts and associated performance of EOS' new PbSe FPA's.

Update on the imaging sensor for GIFTS

Abstract: Remote temperature sounding from the vantage point of Earth Orbit improves our weather forecasting, monitoring and analysis capability. Recent advances in the infrared hyperspectral sensor technology promise to improve the spatial and temperature resolution, while offering relatively quick re-look times to witness atmospheric dynamics. One approach takes advantage of a two-dimensional, imaging Fourier transform spectrometer to obtain a data cube with the field of view along one plane and multiple IR spectra (one for every FPA pixel) along the orthogonal axis. Only the pixel pitch in the imaging focal plane and the optics used to collect the data limit the spatial resolution. The maximum optical path difference in the Michelson FTS defines the spectral resolution and dictates the number of path-length interferogram samples (FPA frames required per cube). This paper discusses the unique challenges placed on the focal plane by the Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS) approach and how advanced focal plane technology is applied to satisfy these challenges. The instrument requires a midwave spectral band from 4.4 to 6.1m to capture the C02 and H20 absorption bands, and an optional VLWIR spectral band to cover from 8.85-14.6m. The paper presents performance data of Liquid Phase Epitaxy (LPE) fabricated HgCdTe detectors and design details of the advanced readout integrated circuit necessary to meet the demanding requirements of the imaging sensor for the GIFTS instrument. Point defects are removed by using a unique super-pixel approach to improve operability for the VLWIR focal plane. Finally, early focal plane performance measurements are reported, including Noise Equivalent Input, responsivity uniformity, output offset stability and 1/f noise knee.

Characterization of Rockwell Scientific LWIR HgCdTe detector arrays

Abstract: Future infrared space missions will undoubtedly employ passively cooled focal plane arrays (T ~ 30K), as well as passively cooled telescopes. Most long-wave detector arrays (e.g. Si:As IBC) require cooling to temperatures of ~ 6-8K. We have been working with Rockwell Scientific Company to produce ≥ 10 μm cutoff HgCdTe detector arrays that, at temperatures of ~ 30K, exhibit sufficiently low dark current and sufficiently high detective quantum efficiency, as well as high uniformity in these parameters, to be interesting for astronomy. Our goal is to achieve dark current below the target value of ~30 e-/s/pixel with at least 60mV of actual reverse bias across the diodes at T ~ 30K. To this end, Rockwell Scientific Company has delivered the first array in a new order, for characterization in Rochester. Recent array deliveries of 10μm cutoff HgCdTe bonded to a Hawaii-1RG multiplexer utilize the smallest capacitance diode type. We present preliminary results on this latest 10 μm cutoff HgCdTe low dark current detector array.

Resonant cavity-enhanced mercury cadmium telluride detectors

Abstract: The next-generation mercury cadmium telluride (HgCdTe) detectors will need to be able to spectrally resolve images to a degree far exceeding that currently available in two or even three color techniques. However, narrow, spectral pass bands will result in very low photon flux impinging on a detector. This paper investigates the use of resonant cavity-enhanced (RCE) detectors as a means of improving signal-to-noise performance of narrow spectral-width infrared (IR) detection systems.

Wide-FOV FPAs for a shipboard distributed aperture system

Abstract: The Navy faces an ever evolving threat scenario, ranging from sub-sonic sea skimming cruise missiles to newer, unconventional threats such as that experienced by the USS Cole. Next generation naval technology development programs are developing “stealthy” ships by reducing a ships radar cross section and controlling electromagnetic emissions. To meet these threat challenges in an evolving platform environment, ONR has initiated the “Wide Aspect MWIR Array” program. In support of this program, Raytheon Vision Systems (RVS) is developing a 2560 X 512 element focal plane array, utilizing Molecular Beam Epitaxially grown HgCdTe on silicon detector technology. RVS will package this array in a sealed Dewar with a long-life cryogenic cooler, electronics, on-gimbal power conditioning and a thermal reference source. The resulting sub system will be a component in a multi camera distributed aperture situation awareness sensor, which will provide continuous surveillance of the horizon. We will report on the utilization of MWIR Molecular Beam Epitaxial HgCdTe on Silicon material for fabrication of the detector arrays. Detector arrays fabricated on HgCdTe/Si have no thermal expansion mismatch relative to the readout integrated circuits. Therefore large-area focal plane arrays (FPAs) can be developed without concern for thermal cycle reliability. In addition these devices do not require thinning or reticulation like InSb FPAs to yield the high levels of Modulation Transfer Function (MTF) required by a missile warning sensor. HgCdTe/Si wafers can be scaled up to much larger sizes than the HgCdTe/CdZnTe wafers. Four-inch-diameter HgCdTe/Si wafers are currently being produced and are significantly larger than the standard 1.7 inch x 2.6 inch HgCdTe/CdTe wafers. The use of Si substrates also enables the use of automated semiconductor fabrication equipment.

Infrared negative luminescent devices and higher operating temperature detectors

Abstract: Infrared LEDs and negative luminescent devices, where less light is emitted than in equilibrium, have been attracting an increasing amount of interest recently. They have a variety of applications, including as a ‘source’ of IR radiation for gas sensing; radiation shielding for, and non-uniformity correction of, high sensitivity staring infrared detectors; and dynamic infrared scene projection. Similarly, infrared (IR) detectors are used in arrays for thermal imaging and, discretely, in applications such as gas sensing. Multi-layer heterostructure epitaxy enables the growth of both types of device using designs in which the electronic processes can be precisely controlled and techniques such as carrier exclusion and extraction can be implemented. This enables detectors to be made which offer good performance at higher than normal operating temperatures, and efficient negative luminescent devices to be made which simulate a range of effective temperatures whilst operating uncooled. In both cases, however, additional performance benefits can be achieved by integrating optical concentrators around the diodes to reduce the volume of semiconductor material, and so minimise the thermally activated generation-recombination processes which compete with radiative mechanisms. The integrated concentrators are in the form of Winston cones, which can be formed using an iterative dry etch process involving methane/hydrogen and oxygen. We present results on negative luminescence in the mid- and long-IR wavebands, from devices made from indium antimonide and mercury cadmium telluride, where the aim is sizes greater than 1 cm ×1 cm . We also discuss progress on, and the potential for, operating temperature and/or sensitivity improvement of detectors, where very high-performance imaging is anticipated from systems which require no mechanical cooling.

I-V modeling of current limiting mechanisms in HgCdTe FPA detectors

Abstract: This paper details significant improvements in current-voltage (I-V) modeling capabilities using an automated iterative non-linear fitting program The properties of a particular infrared (IR) detector's I-V curve are dependent upon the current limiting mechanisms in the device which depend upon the temperature, applied bias, and cutoff wavelength or detector bandgap This model includes ideal diode diffusion, generation-recombination, band-to-band tunneling, trap-assisted tunneling, shunt resistance, and avalanche breakdown as potential current limiting mechanisms in an IR detector diode The modeling presented herein allows one to easily distinguish, and more importantly to quantitatively compare, the amount of influence each current limiting mechanism has on various detector's I-V characteristics Modeling of the trap-assisted-tunneling mechanism leads to an estimate of the density of occupied trap states at a given temperature This model is now routinely applied to Raytheon Vision Systems’ test structures to better understand detector current limitations

Performance limitations of small-format high-speed infrared arrays for active control loops in interferometry and adaptive optics

Abstract: The detector mounted in the VLTI fringe sensor FINITO is a 256x256 HgCdTe array with a cut-off wavelength of 1.9 micron. The same arrays having cut-off wavelengths of 2.5 micron will be used in the tip tilt sensor IRIS and the PRIMA instrument of the VLT interferometer. The arrays are part of an active control loop with integration times as short as a few hundred microseconds. The fringe tracker FINITO uses only 7 pixels of the array. To take advantage of the four parallel channels of the PICNIC multiplexer, the pixels illuminated in each quadrant are positioned at the same location within the quadrants. A noise analysis of the PICNIC array shows that the main sensitivity limitation of the array is contained in the low frequency part of the noise power spectrum. Similar behaviour has been observed with other infrared arrays. In an effort to optimize the unit cell pixel buffer to achieve high speed and low noise, a prototype multiplexer is being developed at Rockwell for adaptive optics. However, low frequency noise may still be the limiting factor dominating the noise performance of infrared arrays. To overcome this noise barrier, detector architectures have to be envisaged which should allow double correlated sampling on shorter time scales than a full exposure. This might be accomplished by some kind of gate in the IR material which allows charge to be shifted from an integrating well in the infrared pixel to a small sensing node capacitance of the multiplexer unit cell buffer.

Charge caching CMOS detector for polarimetry (C 3 Po)

Abstract: C3Po is a concept for a novel array detector concept that is optimized for highly sensitive and precise differential imaging such as needed for astrophysical polarimetry. Chopping between two or more independent image states (such as four linearly independent polarization states) can be performed at speeds in the kHz domain to provide virtually simultaneous images without the need to read out the array at kHz frame rates. This allows the technology to be applied to large arrays with precise, slow readouts. All independent image planes are observed with the same physical pixel on the detector, which renders normalized differences between image planes insensitive to the gain of individual pixels. The detector concept has 100% geometrical fill factor and a quantum efficiency approaching unity. The technology can be applied to silicon to cover the 200-1100 nm wavelength range, and to infrared-sensitive materials such as HgCdTe or InSb for the 1-20 μm wavelength range. While the detector concept has a wide range of potential applications outside of astronomy, we focus here on its application to polarimetric observations of the Sun.

Large-format 0.85- and 2.5-μm HgCdTe detector arrays for low-background applications

Abstract: The demand for large-format NIR arrays has grown for both ground-based and space-based applications. These arrays are required for maintaining high resolution over very large fields of view for survey work. We describe results of the development of a new 2048 x 2048 HgCdTe/CdZnTe array with 20-micron pixels that responds with high quantum efficiency over the wavelength range 0.85 to 2.5 microns. With a single-layer anti-reflection (AR) coating, the responsive quantum efficiency is expected to be greater than 85% from 0.9 micron to 2.4 microns. The modular package for this array, dubbed the VIRGO array, allows three-side butting to form large mosaic arrays of 4K x 2nK format. The VIRGO readout integrated circuit (ROIC) utilizes a Source Follower per Detector (SFD) input circuit with a well capacity of about 2 x 105 electrons and with a read noise of less than 20 e-rms with off-chip Correlated Double Sampling (CDS). Other features of the VIRGO array include 4 or 16 outputs (programmable), and a frame rate of up to 1.5 Hz in 16-output mode. Power dissipation is about 7 mW at a 1 Hz frame rate. Reset modes include both global reset and reset by row (ripple mode). Reference pixels are built-in to the output data stream. The first major application of the VIRGO array will be for VISTA, the United Kingdom’s Visible and Infrared Survey Telescope for Astronomy. The VISTA FPA will operate near 80K. Dark current is less than 0.1e-/sec at 80K. The cutoff wavelength of the HgCdTe detector can be adjusted for other applications. Space applications might include SNAP, the Supernova/Acceleration Probe, which requires a shorter detector cutoff wavelength of about 1.7 microns. For applications which require both visible and NIR response, the detector CdZnTe substrate can be removed after hybridization, allowing the thinned detector to respond to visible wavelengths as short as 0.4 microns.

Characterization of crosstalk in HgCdTe n-on-p photovoltaic infrared arrays

Abstract: In this paper, a theoretical and experimental study is carried out of crosstalk between neighboring devices within a back-side illuminated two dimensional HgCdTe photovoltaic infrared sensing array. Theoretical calculations are performed utilizing Dhar's model, a 2D simulated current approximation to crosstalk. Experimental results stem from spatial photo-response (SPR) measurements, which have been performed on HgCdTe MWIR photodiode arrays. The characterized devices are part of an 8x8 array fabricated using LPE grown p-type HgCdTe, with photodiodes fabricated in-house at The University of Western Australia. A scanning laser microscope is used to measure the spatial photo-response as a function of temperature. The theoretical model uses finite analysis techniques of probabilistic equations describing photogenerated carrier diffusion within the array. The Dhar model is a two dimensional model of simulated currents generated within the array. The basis of this model is the Kammins Fong (KF) model, a simplistic one dimensional representation of similar simulated currents. Inclusion of diffusion characteristics in the Dhar model is shown to result in greater levels of accuracy.

Infrared focal plane array readout integrated circuit with on-chip 14 b A/D converter

Abstract: Transferring the image information in analog form between the FPA and the external electronics causes the disturbance of the outside noise. On-chip A/D converter into the readout circuit (ROIC) can eliminate the possibilities of the cross-talk of noise. Also, the information can be transported more efficiently in power in the digital domain compared to the analog domain. In designing on-chip A/D converter for cooled type high density infrared detector array, the most stringent requirements are power dissipation, number of bits, die area and throughput. In this study, pipelined type A/D converter was adopted because it has high operation speed characteristics with medium power consumption. Capacitor averaging technique and digital error correction for high resolution was used to eliminate the error which is brought out from the device mismatch. The readout circuit was fabricated using 0.6μm CMOS process for 128 x 128 mid-wavelength infrared (MWIR) HgCdTe detector array. Fabricated circuit used direct injection type for input stage, and then S/N ratio could be maximized with increasing the integration capacitor. The measured performance of the 14 b A/D converter exhibited 0.2 LSB differential non-linearity (DNL) and 4LSB integral non-linearity (INL). A/D converter had a 1 MHz operation speed with 100mW power dissipation at 5V. It took the die area of 5.6 mm 2 . It showed the good performance that can apply for cooled type high density infrared detector array.

Very long wavelength (>15 μm) HgCdTe photodiodes by liquid phase epitaxy

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

MWIR detectors on HgCdTe grown by MBE on 3-in. diameter silicon substrates

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

Study of dark current for mercury cadmium telluride long-wavelength photodiode detector with different structures

Abstract: The dark current mechanism of B + implanted n on p planar photodiode and Indium doped n + n p hetero junction mesa photodiode formed in situ by molecular beam epitaxy for Mercury Cadmium Telluride long wavelength detector was compared and analyzed.It was found that n + n p hetero juction mesa photodiode doped in situ had higher zero bias resistance area product ( R 0A ) than n on p planar photodiode in our experiment. By fitting with experimental data, R 0A at different temperature and the dark current at different bias voltage of the two long wavelength devices were calculated theoretically, and some correlated parameters were also achieved.

Spatial and Angular Responsivity Measurements of Photoconductive HgCdTe LWIR Radiometers

Abstract: Several newly developed large area photoconductive (PC) mercury cadmium telluride (HgCdTe) radiometers have been tested for spatial and angular responsivity for the purpose of determining what mode of operation (or radiometric quantity) could provide the lowest measurement uncertainty. An infrared (IR) test facility has been developed for the characterization of long wavelength IR (LWIR) detectors and radiometers for spatial response uniformity in power measurement mode and angular responsivity in both power and irradiance measurement modes. We have measured 34% to 53% spatial response non-uniformities and 1.5% to 10.5% changes in angular power reponsivity at different beam positions within the f/4 field-of-view (FOV) of the PC HgCdTe radiometers. The lowest responsivity uncertainty is achieved when these non-uniform radiometers are operated in irradiance measurement mode, where the incident uniform field of radiation averages out the detector's non-uniformity related uncertainties. The angular response deviation from the cosine function within the 16? FOV of the radiometers dominates the uncertainty budget for irradiance responsivity measurements in the 3??m to 20??m sensitivity range of these working standard devices.

Higher-operating-temperature high-performance infrared focal plane arrays

Abstract: We present results from indium antimonide and mercury cadmium telluride IR detector arrays operating at temperatures above 80K, whilst retaining high performance. Multi-layer epitaxial growth is employed to minimize thermally generated leakage currents, through the use of structures designed to control transport of charge generated outside of the active region to the diode junction and to minimize Auger generation within the active region. This enables an increase in operating temperature of a few tens of degrees in the case of background limited III-V devices, and thermoelectric operation of MCT detectors sensitive to the MWIR band. We also discuss the effects of reverse bias on diodes to actively suppress the Auger generation, and the consequent introduction of 1/f noise. Optical concentrators can be used to minimize the volume of detector material in order to gain further increases in temperature. The concentrators, based on Winston cone designs, are fabricated at each pixel by reactive ion etching directly into the detector material and its substrate, and allow a theoretical reduction in volume of a factor of up to 16. This translates into a potential additional increase in temperature of several tens of degrees.

Mercury Cadmium Telluride for High Operating Temperature Infrared Detectors

Abstract: : High Operating Temperature (HOT) Infrared detectors are required for upgrades of existing Army systems such as the AN/TAS-4 and also for Future Combat Systems. The higher operating temperature for the infrared photon detector could be achieved by suppressing the thermally generated noise. Non-equilibrium mode of operation is an approach to achieve HOT infrared detectors. In this paper, we demonstrate two important milestones that are critical for the development of HOT infrared detectors. First. the growth of high quality (minority carrier lifetime of 7.2 micro-sec at 200K) heterostructures based on mercury cadmium telluride by molecular beam epitaxy for equilibrium and non-equilibrium types of detectors. Secondly, the fabrication of p on n format photovoltaic infrared detectors with very high impedance (R(sub 0)A) on the order of high 10 to the 8th power Ohm-cm2 at 80K are illustrated.

Uncooled long-wavelength infrared photon detectors

Abstract: At present, uncooled thermal detector focal plane arrays are successfully used in string thermal imagers. However, the performance of thermal detectors is modest, they suffer from slow response and they are not very useful in applications requiring multispectral detection. In the paper, a number of concepts to improve performance of photon detectors operating at room temperature are presented. Several types of detector materials are considered: HgCdTe, Sb-based III-V ternary alloys, and type-II InAs/GaSb superlattice. Initial efforts were concentrated on photoconductors and photoelectromagnetic detectors. Recently, advanced heterojunction photovoltaic detectors have been developed. It is shown that uncooled HgCdTe photovoltaic detector can achieve detectivity of 10 9 cmHz 1/2 W -1 at the 8-9 μm range. Potentially the devices can be assembled in large focal plane arrays. This will enable obtaining of NEDT of less than 0.1 K for staring thermal imagers operating with f/1 optics and 30s -1 frame rate.

2k×2k nir hgcdte detector arrays for vista and other applications

Abstract: The demand for large-format NIR arrays has grown for both ground-based and space-based applications. These arrays are required for maintaining high resolution over very large fields of view for survey work. We describe results of the development of a 2048×2048 HgCdTe/CdZnTe array with 20 micron pixels that responds with high Quantum Efficiency (QE) over the wavelength range of 0.85 to 2.5 microns. With a single-layer antireflection coating, the responsive QE is greater than 70% from 0.9 micron to 2.4 microns. Dark current is typically less than 1e - /sec at 80 K. The modular package for this array, dubbed the VIRGO array, allows three-side butting to form larger mosaic arrays of 4K×2nK format. The VIRGO ROIC utilizes a PMOS Source Follower per Detector (SFD) input circuit with a well capacity of about 3×10 5 electrons and with a read noise of less than 20 e - rms with off-chip Correlated Double Sampling (CDS). Other features of the VIRGO array include 4 or 16 outputs (programmable), and a frame rate of up to 1.5 Hz in 16-output mode. Power dissipation is about 7 mW at a 1 Hz frame rate. Reset modes include both global reset and reset by row (ripple mode). Reference pixels are built-in to the output data stream. The first major application of the VIRGO array will be for VISTA, the UK's Visible and Infrared Survey Telescope for Astronomy. Raytheon Vision Systems has completed delivery of 16 Science Grade arrays and four Engineering arrays to VISTA. The VISTA FPA will operate at near 80 K. The cutoff wavelength of the HgCdTe detector can be adjusted for other applications. Space applications include SNAP, the Supernova/Acceleration Probe, which requires a shorter detector cutoff wavelength of 1.7 microns. For applications which require both visible and NIR response, the detector CdZnTe substrate can be removed after hybridization, allowing the thinned detector to respond to visible wavelengths as short as 0.4 microns.

Accurate determination of composition profiles in abrupt MBE grown HgCdTe heterostructures

Abstract: Heterostructured Hg(1-x)Cd(x)Te photodetectors are important for the next generation of high performance Infra-Red (IR) sensing applications. The measurement of the composition and thickness of each layer in double layer HgCdTe heterostructures is examined in this paper, in particular, the use of infrared transmission and Secondary Ion Mass Spectroscopy techniques. Several authors have published models of the optical absorption coefficient and refractive index in HgCdTe, and these models have been assessed on their suitability for use in modelling the infrared transmission characteristics of multilayer HgCdTe films. No data is available for the refractive index of HgCdTe for photon energies around the bandgap energy, so a modified Sellmeier equation has been used to approximate the refractive index in this range. A versatile mathematical model of the infrared transmission of multilayer HgCdTe films is presented, based on the characteristic matrix of each layer. The model is then fit to experimental data, where the composition and thickness of each of the HgCdTe layers are fitting parameters. While some film parameters may be determined with high accuracy from infrared transmission, Secondary Ion Mass Spectroscopy (SIMS) is useful as a complimentary technique which enables the measurement of the composition of the wider bandgap HgCdTe layer in double layer HgCdTe films, as well as measurement of the interface abruptness and layer uniformity. A method of calibrating SIMS data is presented, which gives results consistent with those obtained from infrared transmission fitting. Room temperature infrared transmission spectra and SIMS depth profiles of HgCdTe layers grown by Molecular Beam Epitaxy at the University of Western Australia are presented, and are compared with theoretical composition vs. depth profiles which have been determined using elements of each measurement technique.