T. E. Zipperian

Thin‐film palladium and silver alloys and layers for metal‐insulator‐semiconductor sensors

The addition of Ag to Pd in the gate metal of a metal‐insulator‐semiconductor gas sensing diode can improve the performance and change the selectivity of the sensors for a variety of reactions. Data on the response of diodes with 12 different ratios of Ag to Pd in alloys and layers of Pd and Ag to hydrogen and other gases are reported. Diodes with as much as 32% Ag respond very well to H2 gas and the films are much more durable to high hydrogen exposure than pure Pd films. Improvements in the rate of response and aging behavior are found for certain Ag combinations; others give poorer performance. The presence of Ag on the surface changes the catalytic activity in some cases and examples of H2 mixed with O2 and/or NO2, propylene oxide, ethylene, and formic acid are given. Such selectivity forms the basis for miniature chemical sensor arrays which could analyze complex gas mixtures.

Channel-collector transistors

By merging the channel regions of two-junction field-effect transistors with the collector region of a bipolar junction transistor (BJT), one achieves a quasi-cascode configuration called a Channel-Collector Transistor (CCT). Its terminal properties are those of a modified, improved bipolar transistor. Prototype devices have been fabricated with common-emitter current gain (βF) in excess of 1200 while still maintaining the common-emitter, open-base breakdown voltage (BVCE0) greater than 140 V and the output resistance r0typically greater than 200 kΩ. The present brief describes an efficient, qualitative equivalent circuit for the structure and also presents an experimental device graphically illustrating the CCTs advantages and disadvantages when compared to a conventional BJT.

p‐channel, strained quantum well, field‐effect transistor

A p‐channel field‐effect transistor with a 3.5 μm Cr/Au gate was fabricated from a modulation‐doped GaAs/In0.2Ga0.8As/GaAs quantum well structure. Well‐behaved transistor action was observed at both 300 and 77 K with extrinsic transconductances of 6.2 and 11.3 mS/mm, respectively. Shubnikov–deHaas measurements prove the existence of a two‐dimensional hole gas with a strain‐shifted light‐hole ground state associated with a light‐hole mass of 0.154m0.

Stability of strained quantum-well field-effect transistor structures

Conditions for stability of strained-layer structures and their implications for device fabrication are examined. Structures which have exhibited the best performance to date are found to be thermodynamically metastable (or at best marginally stable) structures, which will restrict the processing steps permissible in the integration of these devices to form complex circuits.<<ETX>>

Confocal resonators for measuring the surface resistance of high‐temperature superconducting films

A quasioptical technique of measuring superconductor surface resistance using a confocal resonator has been developed. The method has advantages of nondestructive analysis, high sensitivity, easy extension to higher frequencies, convenient experimental setup, and flexibility in sample size. Tl‐Ca‐Ba‐Cu‐O high‐temperature superconducting films have been measured with this technique and the measured surface resistances were less than 0.01 Ω at 36.135 GHz and 77 K. The measurements have been performed from 29 to 39 GHz, and all films showed roughly a quadratic dependence of surface resistance with frequency.

GaAs/(In,Ga)As, p‐channel, multiple strained quantum well field‐effect transistors with high transconductance and high peak saturated drain current

GaAs/In0.2 Ga0.8 As structures with two paralleled 10 nm quantum wells, modulation doped from the top, bottom, and middle with Be, have been fabricated into multiple strained quantum well field‐effect transistors (MQWFET’s) with 1×150 μm2 Ti/Au gates and examined both illuminated and in the dark at 300 and 77 K. Measurements on van der Pauw structures fabricated simultaneously with the transistors showed hole mobilities and sheet carrier densities to be 200, 3100, and 8040 cm2/V s, and 5.7×1012, 1.8×1012, and 1.5×1012 cm−2 , at 300, 77, and 4 K, respectively. Shubnikov–de Haas measurements made below 4 K verified the existence of a double‐channel two‐dimensional hole gas with a strain‐shifted light‐hole ground state in the quantum wells with an effective hole mass of 0.15 me . A representative p‐channel MQWFET showed well‐saturated common‐source output characteristics, both illuminated and unilluminated, at all measurement temperatures. Measured peak extrinsic transconductances and peak saturated drain cu...

Be‐implantation doping of GaAsxP1−x/GaP strained‐layer superlattices

We present Hall‐effect measurements of the first localized p‐type doping in GaAsxP1−x /GaP strained‐layer superlattices achieved by implantation of 1×1015 cm−2, 75 kV 9Be+ followed by controlled‐atmosphere annealing at 825 °C for 10 min. The acceptor activation (∼15% at 300 K) and the mobilities in the p regions (∼20 cm2/Vs at 300 K) are consistent with the values expected for type‐converted GaP‐based alloys. Depth‐dependent structural characterization by ion channeling demonstrates that the superlattice structure survived the implantation and annealing without loss of layer strain. These results demonstrate that Be implantation can be applied to produce localized doping in a strained‐layer superlattice system and reflect favorably on the stability of strained‐layer superlattices under particle bombardment and thermal cycling.

Demonstration of an InAsSb strained-layer superlattice photodiode

A photodiode consisting of a p‐n junction embedded in an InAs0.09Sb0.91/InSb strained‐layer superlattice with equal 130‐A‐thick layers was grown using molecular beam epitaxy. This nonoptimized device exhibited photoresponse out to a wavelength of 8.7 μm at 77 K. The resistance and the minority‐carrier diffusion length of the photodiode result in a detectivity (3×109 cm Hz1/2/W) at 7 μm that is within one order of magnitude of the detectivity of the best HgCdTe detectors at that wavelength.

Long-wavelength, InAsSb strained-layer superlattice photovoltaic infrared detectors

Long-wavelength infrared photodiodes were fabricated using InAs/sub 1-x/Sb/sub x//InSb (x=0.82-0.85) strained-layer superlattices (SLSs). These structures can be grown using either molecular-beam epitaxy or metalorganic chemical vapor deposition. These photodiodes display broad spectral responses up to wavelengths greater than or approximately equal to 10 mu m, and detectivities of 1*10/sup 9/ cm-Hz/sup 1/2//W at 10 mu m.<<ETX>>

High photoconductive gain in lateral InAsSb strained-layer superlattice infrared detectors

Both large photoconductive gain and long wavelength photoresponse were observed in lateral photodetectors constructed from type II, InAsSb, strained‐layer superlattices. In a novel, four‐layer superlattice, gain values as large as 90 are reported with a long wavelength cutoff of 8.7 μm at 77 K. The gain is sensitive to the structure and composition of the superlattice, and the sweepout of minority carriers is eliminated with the appropriate contacts.