THE MOLECULAR BEAM EPITAXIAL GROWTH OF HIGH QUALITY GALLIUM-ARSENIDE - ALUMINUM-GALLIUM - ARSENIDE HETEROSTRUCTURES FOR MICROWAVE DEVICE APPLICATIONS (QUANTUM WELLS, IMPURITY, PHOTOLUMINESCENCE, MODULATION DOPING)

The application of molecular beam epitaxially grown single quantum well (SQW) structures to modulation doped field effect transistors (MODFET) requires both high quality thick AlGaAs buffers and thin GaAs layers with excellent electron transport properties. Previous studies have suggested that the quality of GaAs grown on undoped AlGaAs or silicon doped AlGaAs (AlGaAs:Si) is degraded by the effects of interface roughness, carbon incorporation, or lattice strain between the two compounds.;In the present work, the properties of undoped and modulation doped SQWs grown by molecular beam epitaxy (MBE) are analyzed using photoluminescence (PL), Hall measurements, secondary ion mass spectroscopy (SIMS) and transmission electron microscopy (TEM). Structures are grown at high substrate temperatures (680(DEGREES)C) to optimize AlGaAs buffer quality. Very high quality samples with low impurity content are obtained. From PL, full width half maximum (FWHM) linewidths of the heavy hole exciton ranging from 0.6 meV to 1.1 meV for well thicknesses of 175 (ANGSTROM) to 100 (ANGSTROM) respectively are obtained, demonstrating high quality heterointerfaces. Growth at low V:III flux ratios is found to minimize unintentional impurity content. A study of the FWHM linewidth dependence on well thickness suggests that for well thicknesses > 125 (ANGSTROM) the intrinsic GaAs well quality and interface smoothness both contribute to the total linewidth for high quality wells. Studies of modulation doped single quantum wells demonstrate that silicon surface segregation on Al(,0.30)Ga(,0.70)As:Si and incorporation at GaAs growth initiation are the main factors causing the low electron mobilites of this structure. Analysis by SIMS, TEM and PL demonstrate silicon movement while smooth interface quality is still obtained. A PL lineshape analysis suggests the presence of a two dimensional (2D) impurity band in GaAs SQWs grown on AlGaAs:Si. Experimental data on the electrical and optical properties of 2D electron gases in SQWs are presented. Peak 77K Hall mobilities of 140,000 cm('2)/V-s are obtained for 120 (ANGSTROM) wells. The excellent active layer quality and Al(,0.30)Ga(,0.70)As buffer layer quality are demonstrated by the first successful fabrication of a low noise SQW MODFET with a submicron gate exhibiting a cryogenic noise temperature of 10.5K at 8.5 GHz.