Interface-induced origin of Schottky-to-Ohmic-to-Schottky conversion in non-conventional contact to β-Ga2O3

Abstract

β-Ga2O3 is an emerging ultra-wide bandgap semiconductor with wide-ranging applications from civil to military realms. Due to the varied surface states and upward band-bending of β-Ga2O3 with most metals, most of the conventional metal contacts turn out to be Schottky in nature, leading to a paucity of suitable Ohmic contacts to Ga2O3. Transparent conducting oxides (TCOs) offer the flexibility of conduction along with optical transparency, useful especially for optoelectronic devices. Herein, we report on the use of indium-zinc oxide (IZO), a TCO, as a suitable, unconventional contact to β-Ga2O3. The devices show a unique conversion from Schottky to Ohmic by annealing at an optimized temperature of 650 °C, while changing back to Schottky at higher temperatures. At 650 °C, the interface chemistry as studied by x-ray photoelectron spectroscopy changes drastically with band-bending of β-Ga2O3 shifting from upward to downward at the interface leading to a type II band alignment, responsible for the Schottky-to-Ohmic conversion. The results provide evidence of using IZO layer as an alternate contact material to β-Ga2O3 whose behavior as Ohmic or Schottky contact may be tuned by simply varying the annealing temperature and inducing interfacial changes at the semiconductor–electrode interface, while maintaining excellent device resilience. The proposed conducting oxide layer provides an effective strategy toward control and tunability in nature of contacts toward gallium oxide and its applications for high temperature resilience solar-blind photodetectors.