Dean C. Marvin

In/Pt ohmic contacts to GaAs

Graded heterojunction InGaAs ohmic contacts to GaAs have been prepared which show improved electrical and mechanical properties. The improvements result from the use of a thin Pt layer between the In layer and the substrate which controls the reaction of the In and the GaAs. Evidence is also offered that the InAs heterojunction regions are epitaxial.

Holographic solar concentrator

A solar concentrator receives sunlight for generating solar power with the concentrator including holographic optical element (HOE) separators for separating sunlight into separated bands, including HOE concentrators for concentrating the separated bands into concentrated bands, including HOE reflectors for reflecting the concentrated bands as reflected bands onto a multiple junction photovoltaic solar cell for generating the solar power with reduced aberrations of the bands for improved conversion of the solar light into the generator solar power, all of which can be constructed in an integrated structure using spacers, waveguides, and a substrate, where the HOEs use chirp Bragg gratings for reducing optical aberrations of the separated, concentrated, and reflected optical bands, with the option of multiple HOE separators for receiving sunlight from various angles of incidence.The approach selected is the fabrication of holographic optical elements which will focus to either a line or a point. A concentrating mirror is replicated in the hologram, which consists of dichromate gelatin exposed to a laser beam. The dichromate gelatin can be processed to produce a non-uniform microstructure, which gives the hologram a significant waveband width. Even so, it becomes necessary to stack at least three holograms, with each reflecting a different region of the solar spectrum, if we are to reflect most of the solar energy. To achieve high efficiency, it is necessary to obtain adjacent quasi-square waves for the efficiency—wavelength profile of each of the holograms in the stack. Profile information was obtained by the use of a monochromator coupled to a computer. An optical efficiency in excess of 50% was measured for a three-hologram stack. This represents approximately 70% of the efficiency achievable within the limited measuring range of the monochromator. A line-focus holographic concentrator model has been built for demonstration purposes.

Numerical Simulation of SEU Induced Latch-Up

The PISCES-II device analysis program has been modified to perform two-dimensional SEU induced latch-up simulations. The results of the simulations have been compared to cyclotron test data taken on a custom test chip. The comparison indicates that the simulations are accurate for light ions. A description of the latch-up process is also given.

Analysis of transient photoluminescence measurements on GaAs and AlGaAs double heterostructures

The analysis of transient photoluminescence measurements and extraction of carrier recombination lifetimes in GaAs and AlGaAs double heterostructures is discussed. In contrast to recently reported claims, it is demonstrated that even in regions where the measured decay curves show single exponential behavior, the slopes do not, in general, correspond to any single physical carrier lifetime such as the minority‐carrier lifetime. A series of measurements over a range of incident optical intensities is required to extract such lifetimes.

Wide-range fiber-optic strain sensor

A wide-range strain sensor which utilizes optical fiber as the transducing element is reported. This device differs from the well-known microbend type sensor in that a roller chain is used to impose constant curvature bends on the fiber, rather than a corrugated plate which imposes sinusoidal bends in the microbend sensors. This change also leads to a wide range of sensitivity adjustment and a linear calibration curve.

Anomalous solar array performance on GPS

The general issue of degradation of optical surfaces on spacecraft is reviewed in order to understand the observed behavior of the Navstar solar cell arrays. The solar arrays on GPS Navstars 1-6 have shown anomalous degradation during the 5-year mission life and beyond. The departure from predicted performance consists of an extra 2.5% per year degradation in excess of the radiation model estimates. Examination of optical solar reflector (OSR) data from a variety of spacecraft reveals variations in OSR degradation rates which correlate with the vehicle design. These data support the idea that contaminants outgassing from the vehicle are photodeposited on the optical surfaces, leading to degradation of their reflectivity. Contamination data taken from an OSR flown on Navstar 5 are used to predict the solar cell array degradation. The predicted effect of contamination on the array output is consistent with the observed behavior of the five Block I vehicles.<<ETX>>

The advanced solar cell orbit test (ASCOT) flight experiment

The purpose of the ASCOT flight experiment is to evaluate a number of advanced space solar cell designs for use in a high radiation, proton-dominated environment. The motivation for the experiment, the design of the experiment hardware, and a status report are presented.<<ETX>>

Effects of molecular contamination on triple junction solar cells

Space borne high efficiency triple junction solar cells are calculated to be about twice as sensitive to degradation from deposition of films of molecular species (similar to those typically outgassed by spacecraft materials) than are lower efficiency silicon cells. This is a consequence of the facts that 1) sub-cells of multijunction cells are connected in series, so that one of them limits the current through the stack, 2) the current in each sub-cell is lower in multijunction cells than in single junction cells, and 3) the absorptance of the molecular films increases rapidly as wavelength is decreased, effectively concentrating its effect in one sub-cell.

Progress toward technology transition of GaInP/sub 2//GaAs/Ge multijunction solar cells

The objective of the joint WL/PL/NASA Multijunction Solar Cell Manufacturing Technology (ManTech) Program is to scale up high efficiency GaInP/sub 2//GaAs/Ge multijunction solar cells to production size, quantity, and yield while limiting the production cost/Watt (

Directions in US Air Force space power technology for global virtual presence

/W) to 15% over GaAs cells. Progress made by the program contractors, Spectrolab and TECSTAR, include, respectively, best cell efficiencies of 25.76% and 24.7% and establishment of 24.2% and 23.8% lot average efficiency baseline designs. The paper also presents side-by-side testing results collected by Phillips Laboratory and NASA Lewis on Phase I deliverable cells, which shows compliance with program objectives. Cell performance, pre- and post-radiation, and temperature coefficient results on initial production GaInP/sub 2//GaAs/Ge solar cells are presented.