Effects of Annealing on Co/Au and Ni/Au Schottky Contacts on β -Ga 2 O 3

We have investigated the thermal stability of Co/Au and Ni/Au Schottky contacts to Sn-doped ( 2 01) β -Ga 2 O 3 substrates. Current–voltage ( I–V ) and capacitance–voltage ( C–V ) measurements were conducted after sequential annealing treatments totaling > 400 h at 300°C and > 150 h at 500°C in vacuum. For both sets of contacts, the average Schottky barrier heights (SBHs) calculated from the I–V measurements displayed no significant changes and remained within a narrow range throughout the anneals at 300°C. The SBHs calculated from the C–V measurements also remained largely constant for 300°C anneals, except for a modest increase for both contacts for anneal times > 350 h. For 500°C anneals, the I–V characteristics for Ni/Au and Co/Au contacts displayed continual degradation in the electrical behavior after 12 h and 24 h, respectively. Characterizations using scanning transmission electron microscopy, energy dispersive x-ray spectroscopy, and scanning electron microscopy of the samples annealed at 500°C revealed considerable changes in film morphology, interdiffusion, and phase segregation within the contacts. The results suggest the potential for Co/Au or Ni/Au Schottky contacts to be used in Ga 2 O 3 devices at temperatures below, or possibly up to, 300°C, whereas higher temperatures will require modified metallization schemes.