Thermal stability of epitaxial Al/GaAs Schottky barriers prepared by molecular-beam epitaxy

The effect of annealing on the electrical characteristics of epitaxial aluminum/gallium arsenide Schottky barriers prepared by molecular-beam epitaxy has been studied and compared with the annealing behavior of polycrystalline aluminum contacts deposited in a conventional evaporation system. It was found that the epitaxial contacts showed remarkably stable electrical characteristics, the forward characteristics remaining exponential over 6 decades of current after annealing for 1 h at 500 °C, with a slight degradation of n value from 1.01 to 1.02 and a very small recombination component. In the reverse direction, the characteristics improved on annealing, with a reduction in current from 9×10^-10 to 6×10 ^-11 A at a reverse bias of 1 V. In contrast, the polycrystalline contacts showed a pronounced recombination component after annealing, with an increase in n to between 1.05 and 1.09, and a significant degradation in reverse characteristics. Auger depth profiling showed that the epitaxial contacts exhibited a more abrupt interface than the polycrystalline ones in the as-deposited state. After anealing, the epitaxial contacts retained an abrupt interface but the polycrystalline ones became even less abrupt, with considerable in-diffusion of the Al and out-diffusion of the Ga and As. An explanation of these phenomena in terms of increased grain-boundary diffusion in the polycrystalline film is suggested. The technological importance of the results is emphasized.