Ohmic contact formation on n-type β-Ga2O3: Comparative analysis of Ti/Au and ITO/Ti/Au metallization schemes

This study characterizes Ti/Au (20/80 nm) and ITO/Ti/Au (20/20/80 nm) Ohmic contacts on doped n-type β-Ga2O3 epilayers using circular transmission line measurements, current-voltage characterization, Arrhenius analysis, and thermal stability testing. Both contacts achieve excellent specific contact resistivity of 1.3–1.5 × 10−5 Ω cm2 at 498 K (225 °C) with nearly identical activation energies of 74 meV (Ti/Au) and 76 meV (ITO/Ti/Au), confirming thermionic field emission as the dominant transport mechanism controlled by the Ti/Ga2O3 interface. Ti/Au exhibits 40% lower room temperature contact resistivity, while ITO/Ti/Au shows comparable performance at 498 K and provides optical transparency for optoelectronic applications. Thermal stability testing at 550 °C reveals catastrophic degradation of ITO/Ti/Au relative to Ti/Au, establishing maximum safe operating temperatures of approximately 225 °C for ITO/Ti/Au and greater than 300 °C for Ti/Au. Both schemes suit β-Ga2O3 power devices operating at 150–200 °C with selection based on transparency requirements and temperature margins, while recent breakthroughs using ultrathin 5 nm Ti layers (versus traditional 20 nm) demonstrate stable operation up to 600 °C through epitaxial anatase TiO2 formation, suggesting pathways beyond conventional thick Ti layer limits.