Ambient Temperature Operation Research Articles

Observation of below band gap photoconductivity in mercury cadmium telluride

Significant photoresponse beyond the expected cutoff wavelengths has been observed in mercury cadmium telluride (MCT) photoconductive detectors fabricated for ambient temperature operations for applications in 3–5 μm wavelength range. The results have been explained in light of the intervalence excitations from heavy to light hole bands resulting in enhanced conductivity due to a large difference in the light and heavy hole mobilities in MCT. The overall relative photoconductive response has been modelled in terms of both band-to-band and intervalence contributions to the photoconductivity.

Monolithic integration of PbSe IR photodiodes on Si substrates for near ambient temperature operation

Photovoltaic in detectors have been fabricated by a photolithographic process on lead selenide (PbSe) for near ambient temperature operation (200-300 K) in the 3-5 mu m spectral band. The PbSe active layer has been grown by molecular beam epitaxy directly on a Si(111) substrate using a CaF2 buffer layer. The bulk, lateral and surface electrical effects which affect sensor performances have been investigated on variable-area diodes. The dark current is dominated by generation-recombination surface currents which are probably due to an inefficient surface passivation. The lateral collection of photocarriers increases the efficiency of the sensor: at 300 K, the collection length is around 70 mu m and the derived specific detectivity is around 3*109 cm Hz1/2 W-1.

A quantum-dot refrigerator

A cryogenic refrigeration scheme is presented which utilizes the discrete energy levels of quantum dots to customize the electronic Fermi–Dirac distribution, cooling a small but macroscopic reservoir to far below the ambient temperature. Several physical limitations of this scheme are discussed within the context of a model device constructed from a two-dimensional electron gas. These are explored in a simple example where, at an ambient operating temperature of 150 mK, this quantum-dot refrigerator can achieve a cooling power of 1 μW/cm2, a base temperature of 10 mK, and a cooling efficiency of 35%.

Ambient temperature diodes and field-effect transistors in InSb/In1−xAlxSb

InSb and related narrow-gap alloys have many potential applications in addition to the conventional one of infrared detection, provided that ambient temperature operation can be achieved. We report experimental results on multilayer InSb/In1−xAlxSb structures utilizing minority-carrier exclusion and extraction. At room temperature, diodes have R0A values several orders higher than homostructure InSb devices. Negative differential resistance associated with Auger suppression is observed under reverse bias. Enhancement-mode metal-insulator-semiconductor field-effect transistors have near classical output characteristics at 294 K, with a typical transconductance of 34 mS/mm and dynamic range of 23 dB.

The construction of a column‐shaped, thin‐layer ESR spectroelectrochemical cell for use at both ambient and low temperatures in nonaqueous solvents

AbstractThe construction and utilization of a column‐shaped in situ thin‐layer ESR spectroelectrochemical cell for both ambient and low temperature operation is reported. The working electrode is a columnshaped expanded platinum sheet of 9.4 × 4.0 mm that is placed in a 0.25 mm thick column‐shaped, thin‐layer chamber. The solution volume in the thin‐layer chamber is 12 μL, and the total solution volume in the cell ranges between 1 and 3 mL. The application of this cell is demonstrated by time‐resolved ESR spectra for electrooxidized porphyrins in methylene chloride solutions containing 0.3 M tetrabutylammonium perchlorate. The electrochemical behavior of this cell is also demonstrated by the oxidation of ferrocene under the same solution conditions at temperatures between 23 and −75°C. Well‐defined ESR spectra are obtained in as short as 5–10 seconds without data manipulation.

Ferroelectric materials and devices in infrared detection and imaging

Abstract The use of ferroelectric materials for infrared detection and thermal imaging is an established technology. For example, small pyroelectric detector arrays form the basis of the infrared burglar and intruder alarm industry, and the pyroelectric vidicon camera tube has been successfully exploited for thermal imaging in a wide range of industrial and civil applications. Interest in the ferroelectric materials for infrared devices has continued to grow, based on the ambient temperature operation and the potential for low power and cheap detector technologies. In the recent programmes, the attention has turned to research on the new technologies needed to fabricate large hybrid arrays of ferroelectric detectors interfaced with silicon readout ICs. The key items in the hybrid device for the research programmes are firstly the ferroelectric material for the detector wafer, secondly the design of the silicon readout circuit and thirdly the solder bump, flip-chip technology used to fabricate the hybrid. ...

Factors affecting the trapping performance of xenon holdup--filters in nuclear medicine applications.

Activated charcoal traps are used in nuclear medicine departments to capture exhaled radioactive xenon gas. In the present study, the trapping performance of charcoal was investigated for different physical qualities in experimental and clinical situations. Various factors affecting the trapping capacity are identified, such as the charcoal mass, moisture and carbon-dioxide concentrations in the sweep gas, gas-flow rate through the trap, and temperature. Improper drying of the exhaled air prior to passage through the charcoal bed appears to be a critical factor, leading to a much earlier breakthrough of xenon. Commercial xenon traps intended for ambient temperature operation were found to be useful only for a limited number of patients due to an early breakthrough point. By refrigerating the trap, however, a much larger capacity was achieved. If correctly managed, xenon traps constitute a useful alternative for isolating radioactive xenon wastes in clinical and experimental applications.

Life tests of SSI integrated circuits

We present device characteristics obtained from two-dimensional numerical simulations of asymmetric 4H-SiC gate turn-off (GTO) thyristor structures. Material parameters are discussed, and a good comparison with measured results is demonstrated. Current vs voltage characteristics indicate that typical structures have quite good electron injection from the cathode, but hole injection from the anode is weak unless the n-base layer is doped less than 1×1018 cm−3. On the other hand, lowering electron injection at the cathode/p-base junction is important to improve the turn-off gain. The 2000 V blocking structure simulated with lifetimes of τn:τp=100:50 ns does not reach its on-state for current densities less than 6000 A/cm2, but for lifetimes of 400:200 ns, this minimum is reduced to 1 A/cm2. Blocking voltages increased approximately 400 V for a 3 μm increase in the drift region length. Clamped inductive load mixed-mode simulations with a 4H-SiC flyback diode indicate that the peak power during turn-on is only slightly higher than during turn-off when switching a 4 Ω, 5 mH load. Because turn-on times are much shorter than turn-off times, much less power is dissipated during turn-on for both 27°C and 200°C ambient temperature operations.

The role of radiation damage on the current-voltage characteristics of junctions

We present device characteristics obtained from two-dimensional numerical simulations of asymmetric 4H-SiC gate turn-off (GTO) thyristor structures. Material parameters are discussed, and a good comparison with measured results is demonstrated. Current vs voltage characteristics indicate that typical structures have quite good electron injection from the cathode, but hole injection from the anode is weak unless the n-base layer is doped less than 1×1018 cm−3. On the other hand, lowering electron injection at the cathode/p-base junction is important to improve the turn-off gain. The 2000 V blocking structure simulated with lifetimes of τn:τp=100:50 ns does not reach its on-state for current densities less than 6000 A/cm2, but for lifetimes of 400:200 ns, this minimum is reduced to 1 A/cm2. Blocking voltages increased approximately 400 V for a 3 μm increase in the drift region length. Clamped inductive load mixed-mode simulations with a 4H-SiC flyback diode indicate that the peak power during turn-on is only slightly higher than during turn-off when switching a 4 Ω, 5 mH load. Because turn-on times are much shorter than turn-off times, much less power is dissipated during turn-on for both 27°C and 200°C ambient temperature operations.

A thyristor protected against di/dt-failure at breakover turnon

We present device characteristics obtained from two-dimensional numerical simulations of asymmetric 4H-SiC gate turn-off (GTO) thyristor structures. Material parameters are discussed, and a good comparison with measured results is demonstrated. Current vs voltage characteristics indicate that typical structures have quite good electron injection from the cathode, but hole injection from the anode is weak unless the n-base layer is doped less than 1×1018 cm−3. On the other hand, lowering electron injection at the cathode/p-base junction is important to improve the turn-off gain. The 2000 V blocking structure simulated with lifetimes of τn:τp=100:50 ns does not reach its on-state for current densities less than 6000 A/cm2, but for lifetimes of 400:200 ns, this minimum is reduced to 1 A/cm2. Blocking voltages increased approximately 400 V for a 3 μm increase in the drift region length. Clamped inductive load mixed-mode simulations with a 4H-SiC flyback diode indicate that the peak power during turn-on is only slightly higher than during turn-off when switching a 4 Ω, 5 mH load. Because turn-on times are much shorter than turn-off times, much less power is dissipated during turn-on for both 27°C and 200°C ambient temperature operations.

Effects of nuclear radiation on a high-reliability silicon power diode—4. Analysis of reverse bias characteristics

We present device characteristics obtained from two-dimensional numerical simulations of asymmetric 4H-SiC gate turn-off (GTO) thyristor structures. Material parameters are discussed, and a good comparison with measured results is demonstrated. Current vs voltage characteristics indicate that typical structures have quite good electron injection from the cathode, but hole injection from the anode is weak unless the n-base layer is doped less than 1×1018 cm−3. On the other hand, lowering electron injection at the cathode/p-base junction is important to improve the turn-off gain. The 2000 V blocking structure simulated with lifetimes of τn:τp=100:50 ns does not reach its on-state for current densities less than 6000 A/cm2, but for lifetimes of 400:200 ns, this minimum is reduced to 1 A/cm2. Blocking voltages increased approximately 400 V for a 3 μm increase in the drift region length. Clamped inductive load mixed-mode simulations with a 4H-SiC flyback diode indicate that the peak power during turn-on is only slightly higher than during turn-off when switching a 4 Ω, 5 mH load. Because turn-on times are much shorter than turn-off times, much less power is dissipated during turn-on for both 27°C and 200°C ambient temperature operations.

Rapid procedure for liquid scintillation counting of animal tissues using a nitric acid digestion procedure and a dioxane-based scintillator

The development of a liquid scintillator solvent that can hold up to 4.5 ml of H 2O per 10 ml of solvent is described. This solvent consists of 1% butyl-PBD and 6% naphthalene in dioxane. A nitric acid digestion system for use in conjunction with this solvent is applicable to a wide range of animal tissues, is relatively rapid, calls for minimum modification from tissue to tissue, and generally yields colorless counting solutions without need for special decolorization techniques. It must be emphasized that this system was designed for ambient temperature operation and is unusable in refrigerated spectrometers.

Survivability Studies of Lithium Drifted Silicon Detectors under Severe Environmental Conditions

Several lithium drifted silicon, surface barrier detectors were subjected to a variety of environmental conditions. The conditions were primarily those of long term storage under ambient temperature conditions and of long time operation under both ambient and high (+60°C) temperature operation. Use was made of the temperature dependence of the diffusion coefficient of lithium in silicon so that elevated temperatures could be used to decrease the time scale of the tests. Some detectors were also subjected to a series of vibration and shock tests. The entire set of tests was performed in an effort to see if the detectors could withstand the rigors of the Apollo mission. The results of all the tests are given in the paper.

Design of an Electro-Optic Polarization Switch for a High-Capacity High-Speed Digital Light Deflection System

Modulator requirements for an active electro-optic polarization switch to operate in a digital light deflector (DLD) are derived. It is shown that a simple capacity speed product of the form (capacity) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> × (address rate) ≦ (constant) × (driver power) can be derived for both linear and biased quadratic electro-optic modulator materials. The usefulness of this relation is demonstrated by applying it to a biased quadratic electro-optic material (KTN) and two linear electro-optic materials (LiNbO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> and ZnTe). The results indicate that KTN will operate a DLD at a rate of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> random addresses/sec and a capacity of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> addresses with a reactive power of 2.6 watts, a bias voltage of 1200 volts, and a driver voltage of 42 volts, provided, (i) fluctuations in the Curie temperature and ambient operating temperature are held to less than 0.01°C, (ii) some form of ac bias is used to circumvent space charge effects, and (iii) strain and defect-free material meeting these requirements can be grown to a size of at least 1 × 1 × 2 cm. A linear electro-optic material such as ZnTe with a reduced half-wave voltage (unity aspect ratio) in the 2 to 3-kV range (2.5 kV at 6000 Å) will provide 3.6 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> addresses at a rate of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> addresses/sec with a reactive driver power of 10 watts, delivered at a drive voltage of 1250 volts. Experimental results obtained using KTN as a high-speed pulsed light modulator are also presented.

Porous carbon for fuel cell electrodes

Carbon has desirable properties which recommend its utilization as a fuel cell electrode material. Good electrical conductivity and chemical resistance to attack by both acid and alkaline electrolytes coupled with a low inherent cost make carbon attractive as a porous substrate for a diffusion-type fuel cell electrode. Data are presented on porosity, pore size distribution, BET surface area and other physical properties of the porous carbon used as substrates for oxygen and air electrodes. The physical properties of the porous carbon are not independent variables, but rather are interrelated so that optimization of a given property may lead to undesired changes in other properties. Electrochemical performance data including life tests are given showing ambient temperature operation of oxygen electrodes in both acid and alkaline electrolytes.

Cryogenic to ambient temperature operation of circulators for ultra-low-noise applications

Cryogenic to ambient temperature operation of circulators for ultra-low-noise applications