Smooth and continuous Ohmic contacts to GaAs using epitaxial Ge films

Abstract

Ohmic contacts to n-type GaAs have been developed using epitaxial Ge films on GaAs alloyed with Ni overlayers by solid-state diffusion at temperatures of 450–550 °C. The contacts are smooth and continuous, showing no evidence of phase separation or other surface structure. Interdiffusion at the Ge-GaAs and Ni/Ge-GaAs interfaces was examined by Auger electron spectroscopy (AES) sputter profiling techniques. An abrupt profile is observed at both the as-deposited and sintered Ge-GaAs interface. With the presence of a Ni overlayer, significant interdiffusion between Ge and GaAs is revealed by AES profiles. These results, together with the current-voltage (I-V) characteristics of similar contacts prepared on p-type GaAs, indicate the presence of a Ge-doped n+ layer at the Ni/Ge-GaAs interface.