SUPERLATTICE BUFFER LAYERS FOR LOW-DEFECT GAAS EXPOTAXIAL FILMS ON IMPERFECT GAAS SUBSTRATES

THE LACK OF REPRODUCIBLY UNIFORM, LOW-DEFECT GAAS MATERIAL REMAINS A MAJOR OBSTACLE TO THE DEVELOPMENT OF ADVANCED MICROWAVE DEVICE TECHNOLOGIES, ESPECIALLY DIGITAL AND MONOLITHIC MICROWAVE INTEGRATED CIRCUITS. SPIRE PROPOSES TO CIRCUMVENT THE SHORTCOMINGS OF MELT-GROWN GAAS WAFERS BY MEANS OF SUPERLATTICE BUFFER LAYERS, WHICH WOULD ACT AS BARRIERS TO THREADING DISLOCATIONS IN ADDITION TO PROVIDING UNIFORM AND DAMAGE-FREE SURFACES. SPECIFICALLY, THE PHASE I PROJECT OBJECTIVE IS TO FABRICATE GAAS/ALAS AND LOW-MISFIT GAAS/GA(AS,P) SUPERLATTICES AND TO ASSESS THEIR EFFECTIVENESS AS DISLOCATION BARRIERS. THE SUPERLATTICES WILL BE GROWN BY METALORGANIC CHEMICAL VAPOR DEPOSITION (MO-CVD) UPON GAAS WAFERS, WITH THE COMPOSITION OF THE SUPERLATTICE AS THE SOLE PARAMETER TO BE VARIED. THE DISLOCATION DENSITIES IN THE SUBSTRATES AND IN GAAS EPITAXIAL FILMS DEPOSITED ON THE SUPERLATTICE STRUCTURES WILL BE DETERMINED BY ETCH-PIT COUNT AND BY TRANSMISSION ELECTRON MICROSCOPY (TEM). THE INTERACTION OF THREADING DISLOCATIONS WITH THE SUPERLATTICES WILL ALSO BE OBSERVED BY CROSSSECTION TEM, AND THE NUMBER OF INTERFACES PENETRATED BEFORE DIVERSION WILL BE DETERMINED. BOTH SETS OF DATA WILL BE USED TO DERIVE COMPARABLE FIGURES OF MERIT FOR THE DISLOCATION BARRIERS. FINALLY, THE RESULTS WILL BE USED TO DEMONSTRATE THE FEASIBILITY OF SUPERLATTIC BUFFER LAYERS.