Smooth and continuous Ohmic contacts to GaAs using epitaxial Ge films

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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.