Gold on GaAs: Its crystallographic orientation and control on the orientation of the Au-Ga reaction product

X-ray diffraction of a 1500 Å evaporated gold thin film on GaAs(100) was used to study the textures of gold and the Au-Ga reaction product (Au₇Ga₂ or β-(Au-Ga)). Post-deposition annealing up to 450 °C for 30 min was found to enhance the gold orientation with Au(100) GaAs(100) and Au[001]GaAs[001] and weaken the gold orientation with Au(111)GaAs(100) and Au[011]GaAs[011] (and its fourfold rotation twins around GaAs[100]). The gold-rich terminal substitutional solid solution α-(Au-Ga) was observed to begin forming below 350 °C. Dissolution of α-(Au-Ga) at 450-500 °C on heating and precipitation of α-(Au-Ga) on subsequent cooling caused a sharp increase in the orientation with Au(110)GaAs(100) and Au[110]GaAs[011], which has the smallest lattice misfit compared with the other gold orientations. The dissolution and precipitation of α-(Au-Ga) also caused the appearance of aligned rectangular pits. The crystallographic orientation of Au₇Ga₂ (or β-(Au-Ga)) was controlled by the orientation of α-(Au-Ga) that had been enhanced by the dissolution and precipitation of α-(Au-Ga) such that the lattice match between Au₇Ga₂ and gold was nearly perfect on the Au{111} interface planes. A dominant orientation relationship in the Au(111) plane is. Au(111)Au₇Ga₂(110)GaAs(211). Au[110]Au₇Ga₂[001]GaAs[011].