The quantum efficiencies of front and back illuminated indium antimonide photodiodes have been calculated with the aid of a computer model. This model describes the photodiode quantum efficiency, resistance, capacitance and responsivity for any given doping profile and temperature. The calculations show that front and back illuminated devices optimized for high resistance-area products at 77K have low quantum efficiencies when operated at 4.2K. These photodiodes are fabricated diffusion or ion implantation of a p-type layer in an n-type base with ~1 x 1015 cm-3 donors. The mechanism limiting the quantum efficiencies of these "normal" InSb photodiodes at low temperatures is reduced minority carrier diffusion lengths in the base layer. This effect is minimized by reducing the donor concentrations of the n-type base layer to ~ 1 x 1014 cm-3, thereby increasing the depletion layer width, carrier lifetimes and diffusion lengths of photogenerated minority carriers. High quantum efficiencies from 1-5 microns can then be achieved at 4.2K with front illuminated photodiodes provided that the p-type layer thickness < 2 microns. High quantum efficiencies may also be achieved at low temperature with back illuminated devices fabricated from high purity base layers as thick as ~10 microns provided that the surface recombination velocity < 102 cm/sec. or the base layer is depleted by reverse biasing the photodiode.

(Hg,Cd)Te heterostructures have been grown liquid phase epitaxially from tellurium rich solutions on CdTe and (Cd,Zn)Te substrates. Both MWIR detectors sensitive in the 3-5 μm spectral region and LWIR detectors sensitive in the 8-14 µm spectral region have been fabricated in the heterostructures. Detectors with high RoA (low noise) and high quantum efficiency (high signal) have been fabricated. For the MWIR detectors, quantum efficiency in excess of 75 percent and RoA values in excess of 107 ohm cm2 at 80K have been demonstrated for λCo ~ 5.5 µm. For the LWIR detectors RoA values of ~ 106 ohm cm2 have been demonstrated at 40K for λCo ~ 11 μm. A correlation of the trap energies established via carrier lifetime and DLTS measurements with the depletion width - capacitance data indicates the p-n junction to be located at the heterostructure interface.

Variable temperature Hall and resistivity measurements have been used to monitor the changes in carrier behavior in p-type Hg1-xCdxTe when boron ions are implanted through photochemically deposited SiO2. The formation of an n-type layer is demonstrated. Quantitative and non-destructive determinations of the absolute 10B concentration and distribution has been obtained by the novel method of neutron depth profiling. As expected, the boron distributions in the SiO2 films and Hg1-xCdxTe are strongly dependent upon the ion implant energy. However, negligible changes in the boron depth profiles were found after 200°C anneals. The present results are briefly related to the performance behavior of mid-wavelength infrared (MWIR) sensors produced via generic ion implantation procedures.

Infrared systems for the future include a variety of device configurations. The most studied system is the hybrid focal plane array consisting of a photovoltaic CdHgTe (PV CMT) matrix interconnected by metallic bumps to a CCD silicon chip.CCD devices are more versatile than other silicon circuits, they can be operated in Time, Delay, and Integration mode (TDI) for scanned imaging or in staring mode. But CCD requires high impedance PV detector for direct injection in CCD wells with high coupling efficiency. An other critical performance needed for detectors is low l/f noise for high detectivity at low frequencies. The present work describes recent results obtained on PV CMT detectors and their coupling to CCD circuits.

Recent advances in detector fabrication techniques at Cincinnati Electronics Corporation have made possible high quality Indium Arsenide (InAs) photovoltaic detectors. InAs detectors are an alternative to Indium Antimonide (InSb) detectors when the wavelength of interest is less than 3.5 microns. InAs photovoltaic (PV) detectors offer the flexibility of thermo-electric cooling available with photoconductive detectors such as lead sulfide without sacrificing speed. Recent advances in detector fabrication techniques have made off-mesa bonding possible. These advances will be discussed below as well as their effect on detector performance. Responsivity and noise data at various operating temperatures will be presented as well.

Photograde cadmium sulphide useful for sintered polycrystalline cadmium sulphide photoconductive cells as also for solar cells can be prepared by a simple chemical reaction between a soluble cadmium salt and thiourea in an aqueous alkaline solution by optimising the pH, temperature and concentration of the constituents in the bath. The precipitated cadmium-sulphide after drying at 120°C was found to result in a photograde quality of 99.999% pure cadmium sulphide as estimated by atomic absorption spectrophotometer. Details are given in this paper, of the process of preparation of CdS powder, screen printing and sintering the cadmium sulphide layers to give finally the photoconductive cell which gave on irradiation a change in the resistance of six to seven orders. The sintering technique and the mechanism of the reaction resulting in high photosensitivity of the layer obtained are discussed in detail.

Blocked-Impurity-Band (BIB) extrinsic silicon (Si:As) detectors have demonstrated high sensitivity and quantum efficiency in the long wavelength infrared (LWIR) spectral region (to 28 microns) as well as wide frequency response, low optical crosstalk, nuclear radiation hardness, and stable, predictable performance. Furthermore, it has been demonstrated that SWItched mosFET (SWIFET) multiplexers provide a low noise readout approach for use with BIB detectors. This paper describes the state-of-the-art of multiplexed BIB detector hybrid focal plane arrays (HFPAs). The principle of operation and performance of optimized BIB and Back Illuminated BIB (BIBIB) detectors are presented. The SWIFET multiplexer, including necessary circuitry for BIBIB detector readout, has been designed and fabricated using a newly developed process for cryogenic (<20K) MOS electronics which avoids anomalies (lack of device isolation, excess noise, and long time constants) associated with conventional silicon processes. A description of the design and operation of this multiplexer is given. A number of uniform, highly responsive, 500 element HFPAs have been fabricated and their performance evaluated. The characterization measurements, to be described in the paper, include evaluation of detector dark current, responsivity, noise for various operating conditions, and uniformity of array characteristics. The results obtained and presented demonstrate that focal plane arrays with excellent, unprecedented, LWIR performance have been realized with Blocked-Impurity-Band detector technology.

The status of development and characterization tests of integrated infrared detector array technology for astronomical applications is described. The devices under development include intrinsic, extrinsic silicon, and extrinsic germanium detectors, with hybrid silicon multiplexers. Laboratory test results and successful astronomical imagery have established the usefulness of integrated arrays in low-background astronomical applications.

By combining high-quality mesa photovoltaic indium antimonide detector material with a silicon x-y FET switch multiplexer, a useful infrared area detector has been developed. This device is intended for low-background applications, where high sensitivity is required. Initial characterization of the detector at 80 K showed a KTC limited read noise of less than 1,000 electrons, good dark current, responsivity uniformity, and a maximum readout rate of 10 MHz. The hybrid mating technology has sufficient precision to allow expansion to a 256 x 256 format. The dark current in the detector material is sufficiently low to allow full-frame integration, even with arrays as large as 256 x 256 elements.

A new chip organization for CCD multiplexers to increase the cell capacity is discussed. The chip uses the interlaced readout scheme, the MCCD and the storage/transfer common electrode configuration. These three techniques triple the conventional cell capacity. The CCD multiplexer is source-coupled with a 64 x 64 element HgCdTe photovoltaic array for 3-5 μm spectral region. The cell size of the CCD is 100 x 50 μm. The detector element pitch is 50 μm. The multiplexer has the charge handling capability of 1.1 x 107 electrons/cell. A 50 dB dynamic range is obtained for all 64 x 64 elements with 8% offset variation against 300 K background radiation and 14% responsivity variation. The mean detectivity D*λρ is 1.8 x 1011 cmHz1/2/W at peak wavelength of 4.7 μm. This IRCCD realizes wide dynamic range without sacrificing detectivity.

Earth imaging from satellite in the Short Wave Infrared (SWIR) band (1.55 - 1.70 µm) is of primary importance for agriculture monitoring. The french space agency (CNES) has decided to incorporate a SWIR band in the next generation of the SPOT family. The development of the SWIR hybrid focal plane has been carried on at THOMSON since 1984, on the basis of the visible bands specifications.

We discuss a newly operational CCD imaging system optimized for the near infrared. The CCD is a front-side illuminated, three-phase, 385 x 578 GEC chip. The system is run by an LSI-11/23 computer with a FORTH language operating system. Hardware control signals are sent via a CAMAC interface. The important parameters characterizing the CCD are discussed. Finally, we describe some recent broadband observations of the interacting galaxies Markarian 171 made with the Mt. Lemmon Observatory 1.5 meter telescope.

Recent developments and advancements made in photocathode, MCP and phosphor screen technology are reviewed in light of current requirements in the UV and IR regions of the electromagnetic spectrum. The paper covers such topics as the spectral sensitivity, noise and operational characteristics of photocathodes; MCP gain and noise characteristics; resolution, bandwidth and noise characteristics of image tube phosphors; gated image tubes; and hybrid image tubes for optical communication. Finally, imaging with intensified CCD and CID cameras and multi anode MCP's are discussed.

The problem of deconvolution of the point source response function (PSF) for two dimensional imaging infrared arrays is addressed. A variety of phenomena can lead to PSF degradation ranging from atmospheric turbulence to the array itself. The maximum entropy (MEM) algorithm is used to demonstrate that substantial image quality improvements are possible in the case of a PSF which is degraded by electronic rather than optical smearing. This result implies that IR arrays need not have perfect or even very good pixel-pixel crosstalk rejection ratios for use in astronomy.

Comparison measurements of low level infrared radiation at 1064 nm wavelength of the modified Rj-7000 series radiometer (hereafter termed MRj), custom manufactured by Laser Precision Corporation, were performed with the NBS P-3 low level pulsed laser radiometer constructed at the National Bureau of Standards, Boulder, Colorado. A brief description of these instruments and measurement data are reported in this paper. This is considered of interest for those engaged in the design of radiometers or associated with low level monochromatic performance measurements used with laser ranging and designating systems and test sets. Due to time constraints, interest was focused on the practical lower limit signal-to-noise measurement capability of the MRj radiometer. Data obtained indicate that this radiometer, which is essentially the conventional model specially fitted with an aperture wheel, a reflex mirror, and telescope assembly featuring a 10 cm diameter collecting lens, has a practical lower limit measurement capability of approximately 10 fJ/cm2. This is essentially a few orders of magnitude greater in sensitivity than the conventional, unmodified version, and is in agreement with the theoretical gain obtained using a lens of this size. These results were obtained by comparing the MRj measurements with those utilizing a conventional Laser Precision radiometer without the telescope assembly, in the region of 10-12 J/cm2 and the NBS P-3 in the range of 10-13 J/cm2 to 10-16 J/cm2. A nominal 1064 nm wavelength laser simulator LED was placed at the focal point of a 12.7 cm diameter lens of 60 cm focal length to provide a collimated source of approximately 15 ns FWHM pulse length with a PRR of 30 Hz. It was also noted that the LED output power decreased with increasing pulse repetition rate which was correlated with NBS P-3 radiometer observations between 30 Hz and 125 kHz.

This paper presents the results of an analysis of point source location accuracy and sensitivity as a function of focal plane geometry, optical blur spot, and location algorithm. Five specific blur spots are treated: gaussian, diffraction-limited circular aperture with and without central obscuration (obscured and clear bessinc, respectively), diffraction-limited rectangular aperture, and a pill box distribution. For each blur spot, location accuracies are calculated for square, rectangular, and hexagonal detector shapes of equal area. The rectangular detectors are arranged on a hexagonal lattice. The two location algorithms consist of standard and generalized centroid techniques. Hexagonal detector arrays are shown to give the best performance under a wide range of conditions.

Large area, HgCdTe MW photovoltaic detectors have been developed at Honeywell Electro-Optics Division for the NASA-HALOE instrument. This instrument is scheduled for operation on the Upper Atmospheric Research Satellite (UARS). The photodiodes will be TE cooled and were designed to operate in the 5.1 μm - 5.4 μm band at 185 K to measure Nitric Oxide (NO) concentrations in the atmosphere. To achieve the D* goal of 6 x 109 cm-Hz1/2/W and to meet the spatial responsivity uniformity specification of ± 5% across the 0.6 mm diameter, active area required 15 μm thick devices and a full backside common contact,. Reflections from the backside contact doubled the effective thickness of the detectors. Optical interference from reflections was eliminated with a dual layer front surface A/R coating. Bakeout reliability was optimized by having Au metallization for both n and p interconnects. Detailed performance data and a model for the optical stack are presented.

Expert system techniques have been applied to a parameter adjustment problem of practical importance. Charge-coupled device (CCD) technology is being pushed to the limits in new flight electronics systems. These complex, solid-state devices require continuous adjustment and monitoring to maintain near optimal performance. Although human experts can make the sensitive adjustments needed, to have them do so is neither feasible nor cost effective. Each CCD array has nearly 30 analog inputs that control its behavior. A simple expert system has been written that performs the adjustments to bring the CCD to near optimal performance with respect to three CCD parameters: (1) bucket capacity, (2) charge transfer efficiency, and (3) noise. The system is written in FORTRAN and runs on an IBM XT, interfaced with an HP1000 computer. The second machine actually controls the analog hardware, which, in turn, interfaces with the CCD. The knowledge of device physics has been captured in the form of facts. The heuristic knowledge of adjustment order and magnitude has been represented in the form of rules. Weekly meetings over a 3-month period between the experts and the knowledge engineer supplied the necessary knowledge. The current system improves the CCD array to a higher level than that achievable by the human expert, and in considerably less time.

A Michelson interferometer spectrometer using a flexural pivot suspension for the moving mirror was fabricated for use at 20° K as part of the CIRRIS 1A experiment. The spectral range 2.5 to 25 μm is achieved using a potassium bromide beamsplitter. The softness of the beamsplitter material required special mounting care to preserve beamsplitter flatness while undergoing the strain of being cooled and the shock and vibration of the shuttle launch. Five various sized elements in the arsenic-doped-silicon focal plane provide for tradeoff of sensitivity, spatial and spectral resolution capabilities. A redundant position reference system uses optical fibers to couple optical power from HeNe lasers through the vacuum/cryogenic interface into the interferometer optics where it travels antiparallel to the infrared signal. An alignment system using geared stepper motors provides capability of realignment in space. An eight-position filter wheel is used to enhance the out-of-band signal rejection to enhance high sensitivity in the presence of strong infrared emitters. The interferometer is mounted inside of a high-off-axis rejection telescope to enable measurement of the earth limb emissions. The telescope is cooled to 20° K using supercritical liquid helium.