L. Ralph Dawson

Neutron Damage Equivalence for Silicon, Silicon Dioxide, and Gallium Arsenide

Displacement- and ionization-energy transfers to Si, SiO2, and GaAs as functions of incident neutron energy were calculated using new cross section data and fine group structure in the NJOY code system. Neutron spectra determinations for several reactor neutron environments were made using new activation cross sections and a new technique with the SAND II code. Measurements of carrier removal rates in GaAs and of Si transistor gain degradation were made in representative neutron environments. Experimental results are compared to damage ratios predicted with the new spectra and NJOY displacement functions. For fission-like spectra, calculated Si damage ratios are in good agreement with those determined with ASTM E722-85 and with measured transistor damage ratios. Significant differences are found between Si NJOY and ASTM E722-85 for 14-MeV-to-reactor neutron damage ratios where NJOY gives better agreement with experimental data reported in the literature. In GaAs 14-MeV-to-reactor experimental damage ratios are smaller than predicted by calculated displacement ratios. This suggests that a more complex model of damage for majority carrier removal in GaAs is required. The use of incorrect damage functions is shown to adversely affect simulation fidelity in some representative neutron environments.

Recent Advances in Gallium Phosphide Junction Devices for High-Temperature Electronic Applications

Recent advances in gallium phosphide technology are reviewed as they relate to high-temperature (T > 300°C) device applications. The electronic properties and materials aspects of GaP are summarized and compared to silicon and gallium arsenide. Minority-carrier unction devices are discussed as one area where this technology could have wide application. In this light, the high-temperature operation of two junction devices, a diode and a bipolar junction transistor (BJT), are displayed. The GaP diode is observed to provide excellent rectification properties with very low leakage over the full temperature range from 20°C to 400°C (< 3x10 -3A/cm2 at VR = 3 V, T = 400°C) and has demonstrated stable operation under bias for over 1000 h at 300°. The bipolar transistor has demonstrated constant current gain (6 < ß B < 10) and very low collector-base leakage for temperatures up to 450°C (ICO 80 µA at VCB = 3 V, T = 450°C). The contacting technology to GaP is identified as one area where additional work is necessary.

MBE growth of strained-layer superlattices and quantum wells

Abstract The use of strain in superlattice and quantum well semiconductor structures to produce properties not available in bulk alloys has become important in the design of advanced electronic devices. One such system is the InAsSb strained-layer superlattice, in which tensile strain parallel to [100] interfaces results in lowering of the energy gap, enabling the fabrication of detectors with cutoff wavelength in excess of 12 μm. We discuss the molecular beam epitaxial growth of alloy and superlattice materials suitable for such structures and characterization of materials with significant optical absorption beyond 12 μm.

Microstructural evaluation of strained multilayer InAsSb/InSb infrared detectors by transmission electron microscopy

InSb/InAsSb strained layer superlattices (SLS) were grown on (001) InSb substrates by molecular beam epitaxy at 425 °C. The active device consisted of an InAs0.15Sb0.85/InSb superlattice region embedded within a p‐i‐n junction. The large lattice mismatch between the active device and the substrate required the growth of a buffer. InAs0.15Sb0.85/InSb SLS, where the average As content was gradually increased, was used as a buffer. The buffer structure was varied to probe its microstructural effect on the capping device. Three distinct approaches (A, B, and C) were used to grow the buffer. Approach A was a four‐step buffer where the average content of As in the superlattice was increased in four equal composition steps. This approach led to a crystal with an extensive network of threading dislocations and microcracks. Approach B was to change the average composition in five equal composition steps, thereby decreasing the misfit at the interfaces between composition steps. This led to a decrease in the threading dislocation density but microscopic cracks were still evident. The last approach (C) was to employ migration enhanced epitaxy (MEE) for the growth of the five‐step buffer. Samples grown by employing MEE revealed no microcracks but they contained a high density of unusual ‘‘wiggly’’ dislocations at the buffer/device interface. Detailed microstructural analysis by transmission electron microscopy is presented.

Optical phase conjugation in InGaAs/GaAs multiple quantum wells at 1.06 μm wavelength

The observation of phase conjugation in InGaAs/GaAs multiple quantum wells at 1.06 μm wavelength is reported on. The effective nonlinearity of the sample used in our experiments was measured to be χ(3)=10−7 esu. The nonlinearity is induced by the saturation absorption due to band filling and exciton bleaching. The saturation intensity is 1.3 kW/cm2.

Photoluminescence Studies Of InGaAlAs Quaternary Alloys

Photoluminescence data are used to obtain the concentration and temperature dependence of the bandgap energies of epitaxial layers of quaternary alloy In Ga Al As for Al concentrations less than 0.6. The samples were grown by MBE without an intervening buffer layer. For an In concentration of 0.1, the transition from a direct to an indirect bandgap material occurs at Al concentration of about 0.5. Coefficients of the temperature dependence of the bandgap energy are also presented.