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We have investigated the thermal stability of Co/Au and Ni/Au Schottky contacts to Sn-doped ( 2 ¯ 01) β-Ga2O3 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 Ga2O3 devices at temperatures below, or possibly up to, 300°C, whereas higher temperatures will require modified metallization schemes. [ABSTRACT FROM AUTHOR]

Heteroepitaxial films of Ga2O3 were grown on c-plane sapphire (0001). The stable phase β-Ga2O3 was grown using the metalorganic chemical vapor deposition technique, regardless of precursor flow rates, at temperatures between 500°C and 850°C. Metastable α- and ε-phases were grownwhen using the halide vapor phase epitaxy (HVPE) technique, at growth temperatures between 650°C and 850°C, both separately and in combination. XTEM revealed the better lattice-matched α-phase growing semi-coherently on the substrate, followed by ε-Ga2O3. The epitaxial relationship was determined to be [1100] ε-Ga2O3 || [1120] α-Ga2O3 || [1120] α-Al2O3. SIMS revealed that epilayers forming the ε-phase contain higher concentrations of Cl introduced during HVPE growth. [ABSTRACT FROM AUTHOR]