STRUCTURAL ASPECTS OF NONSTOICHIOMETRY AND HEAVY DOPING OF GAAS

A novel X-ray diffraction method using X-ray quasi-forbidden reflection (XFR) intensity measurements has been developed for the analysis of structural features of both non-stoichiometry and heavy doping in GaAs. Non-stoichiometry of the order of 10(-4) with higher atomic concentrations in the arsenic atomic plane was found for liquid-encapsulated-Czochralski (LEC) grown bulk GaAs, which has a close correlation with etch pit density. The XFR method was also successfully applied to direct analysis of the lattice location of doped impurities and microscopic strain around them for aluminum, indium, zinc, silicon and carbon dopants. In films deposited by molecular beam epitaxy (MBE) onto (100) and (111)B substrates, most doped silicon atoms occupy gallium sites even at high doping concentrations up to [Si] almost-equal-to 10(20) cm-3, and the carrier saturation is due to Si(Ga) complexes. Further, occupation sites of silicon depend on the substrate orientation, and growth on a vicinal surface of (111)A results in a drastic change in conduction type. In metal-organic MBE grown GaAs, nearly complete activation of carbon atoms as acceptors and microscopic strain around C(As) were directly observed up to carrier concentrations of 5 x 10(20) cm-3.