Annealing studies of Au/GaAs and Al/GaAs interfaces using a variable energy positron beam

Abstract

Various thicknesses of Au and Al have been evaporated onto semi-insulating GaAs(110) to form Schottky contacts, which have been subject to different annealing conditions. A variable energy positron beam has been used to probe the metal-semiconductor interfaces by observing the Doppler broadening of the annihilation radiation. The data are well fitted by a three-layer model, namely the metal layer, the interface region and the GaAs bulk. The interfacial region is attributed to the intermixing of the atoms and the formation of new phases occurring at the interface. For the Au/GaAs samples, the interfacial width was observed to increase with increasing annealing temperature and this is attributed to the increase of elemental intermixing at the interface. From the trend of the Doppler broadening signal on annealed samples, we infer that the processes of increasing interfacial order (decreasing S) (such as grain enlargement and vacancy removal) are in competition with the process of decreasing interfacial order (increasing S) (such as vacancy creation through atomic interdiffusion). For Al/GaAs, the interfacial width remained effectively constant up to the annealing temperature of 400°C. From the Doppler broadening signal, the annealing on the interfacial order was found to be metal thickness dependent. This observation has tentatively been explained by the above two competition processes and the grain boundary diffusion of atoms at the Al/GaAs interface. © 1995.