X-ray diffraction (pole figure) study of the epitaxy of gold thin films on GaAs

X-ray diffraction (pole figure) measurements were made on gold thin films (300-2300 Å) evaporated on GaAs{111} and GaAs{001} to investigate the heteroepitaxy and twinning of the gold films and the chemoepitaxy of Au₇Ga₂ on GaAs. For both GaAs orientations the epitaxial relatiobship (hkl)_Au[hkl]_Au// (hkl)_GaAs[hkl]_GaAs was observed for all values of h, k and l. In addition, twin orientations were observed. For GaAs{111}, fourfold rotation twinning about the Au[111] direction resulted in four azimuthal orientations: [112]_Au // [112]_GaAs, [112]_Au // [112]_GaAs, [112]_Au // [110]_GaAs and [112]_Au // [110]_GaAs. For GaAs{001}, reflection twinning with the four Au{111} planes as twinning planes resulted in four other orientations with Au(001) at approximately 71° from GaAs(001). The relative amounts of the twins depended on the substrate temperature, the film thickness and the deposition rate. Chemoepitaxy was observed for Au₇Ga₂ on GaAs{111}; the epitaxial relationship was (111)_Au / (0110)_Au7Ga2 // (111)_GaAs, and Au₇Ga₂[0001] was off by 10° from GaAs[110], toward GaAs[011], i.e. Au₇Ga₂[0001] was off by 10° from Au[110], toward Au[011]. This relationship corresponds to a perfect lattice match between Au₇Ga₂ and gold.