Effect of annealing process parameters on N-GaAs ohmic contacts

Ni/Ge/Ni/Au multi-layer metal electrodes were prepared on N-GaAs substrate by electron-beam evaporation to investigate the effect of annealing process parameters on N-GaAs ohmic contacts. In the annealing temperature range of 370 °C to 430 °C, the metal-semiconductor contact was found changing from Schottky contact to ohmic contact as the annealing temperature was above 380 °C. Specific contact resistivity of n-GaAs samples firstly decreased and then increased with the increasing of annealing temperature, and the minimum specific contact resistivity of 3.3 × 10−5 Ω·cm2 was formed at 420 °C annealing for 80 s. Although the specific contact resistivity of the metal-semiconductor contact performed satisfactorily, the surface morphology of the n-GaAs metal electrode was found having metal shrinkage after annealing. The formation mechanism of ohmic contact was qualitatively explained by the elements diffusion under different annealing parameters, which were confirmed by the comparative analysis of SEM and EDX results.