Electrical and Material Characterization of the Stability of ALGaAs and GaAs Planar Doped Structures
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ELECTRICAL AND MATERIAL CHARACTERIZATION OF THE STABILITY OF ALGAAS AND GAAS PLANAR DOPED STRUCTURES Larry P. Sadwick* and Dwight C. Streit" *Department of Electrical Engineering, Merrill Engineering Building, University of Utah, Salt Lake City, Utah 84112 **TRW Electronic Sysytems Group, One Space Park, Redondo Beach, California 90278
ABSTRACT In this work we have studied the effects of silicon planar doping on the electrical and optical properties of GaAs, and the effects of rapid thermal annealing on AIGaAs planar-doped structures. MBE-grown GaAs epilayers with multiple planar-doped layers displayed a 1.2 eV photoluminescence peak, presumably due to gallium vacancy - donor complexes, for samples with nominal silicon sheet densities much greater than measured charge densities. The Hall mobilities of these samples were also reduced compared to both uniformly-doped and planar-doped structures whose silicon areal densities were more nearly equal to measured sheet charge densities, although X-Ray rocking curves were nearly identical in all cases. Planar-doped AIGaAs Schottky diodes had nearly ideal electrical characteristics. Rapid thermal annealing of the planar-doped structures before fabrication increased the diode ideality factor from n=1.06 to n=1.60, seriously degraded the saturation current and breakdown voltage, and increased the doping profile FWHM from 60A to 170A.
INTRODUCTION The demonstrated improvement in device performance for planar-doped HEMTs has prompted renewed interest in this material structure. Recently Schubert et. al. [1,2] have used planar-doped structures as a tool to study the diffusion of atomic silicon in GaAs and AIGaAs by capacitance-voltage (C-V) measurements on as-grown and annealed samples. In this work we use the C-V technique to investigate silicon diffusion in AIGaAs planar-doped samples, and also characterize the electrical parameters of the diodes before and after rapid thermal annealing. In addition we measure the effects of planar-doping on the Hall mobility, photoluminescence spectra, and X-Ray rocking curves of MBE-grown GaAs.
EXPERIMENTAL Two sets of planar-doped samples were grown and analyzed for this study. The epilayers were all grown at 600C under arsenic stabilized conditions in Varian Genii MBE systems. The first set of samples were designed for analysis by photoluminescence, double-crystal X-Ray diffraction and Hall-effect measurements. All of these samples are 5000A thick GaAs epilayers, bound by thin AIGaAs cladding layers so as to minimize surface, interface and substrate contributions to the photoluminescence spectra, and were grown on semi-insulating GaAs substrates. The second set of samples were designed for C-V and I-V characterization before and after rapid thermal annealing, and were grown on n+ GaAs substrates.
Mat. Res. Soc. Symp. Proc. Vol. 163. c1990 Materials Research Society
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Planar-doped GaAs The structure of the first set of samples is summarized in Table I, along with the Hall-effect results. Sample 1 is a nominally-undoped reference s
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