Temperature Dependent Performance of ITO Schottky Contacts on ?- Ga2O3

Sputtered Indium Tin Oxide (ITO) was used as a rectifying contact on lightly n-type (n~10¹⁶ cm^-3) β- Ga₂O₃ and found to exhibit excellent Schottky characteristics up to 500K, with no thermally-driven degradation to this temperature. The barrier height extracted from current-voltage characteristics was 1.15 eV at 300K and 0.78 eV at 500K, with thermionic behavior of charge carriers over the image force lowered Schottky barriers dominating the carrier transport at low temperatures. The barrier height is close to that expected from the work function of ITO. The breakdown voltages were 246, 185 and 144 V at 300, 400 and 500K, respectively. At 600K, the diodes suffered irreversible thermal damage. The diode on/off ratio was >10⁵ for reverse biases up to 100V. At higher reverse voltage, the current shows an I ∝ Vⁿ relationship with voltage, indicating a trap-assisted space-charge-limited conduction (SCLC) mechanism. We observed this SCLC relation when the reverse voltage was larger than 100 V for 300 K and 400 K and at <100V at 500K. The barrier height at room temperature is 1.15 eV and fits a trend observed for metal contacts on the (100) orientation that correlated metal work function with the electron affinity of the semiconductor. These transparent contacts will be useful in optically-triggered Ga₂O₃ power devices and they exhibit thermally stable barriers up to ~500K.