Evidence for the formation of n(+)-GaAs layer in Pd/Ge ohmic contact to n-type GaAs

Microstructural reactions of PdGe ohmic contact to n-type GaAs were investigated using x-ray diffraction, Auger electron spectroscopy, and slow positron beam. The results were compared with electrical properties to interpret the ohmic contact formation mechanism for the Ge/Pd/n-type GaAs system. The lowest contact resistance of 1.7 Ohm mm and the formation of a PdGe compound are observed at the annealing temperature of 240 degrees C. Slow positron beam results show that Ga vacancies are produced below PdGe during the formation of PdGe ohmic contact to n-type GaAs. This means the existence of n(+)-GaAs layer below PdGe because Ga vacancy concentration increases with n-type impurity concentration. This supports that the n(+)-GaAs layer is a regrown layer decomposed from PdxGaAs containing excess Ge atoms during annealing. (C) 1997 American Institute of Physics.