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 Ω mm and the formation of a PdGe compound are observed at the annealing temperature of 240 °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 Pd_xGaAs containing excess Ge atoms during annealing.