Thermal Stability of Transparent ITO/n-Ga₂O₃/n+-Ga₂O₃/ITO Rectifiers

The thermal stability of n/n+ β-Ga2O3 epitaxial layer/substrate structures with sputtered ITO on both sides to act as rectifying contacts on the lightly doped layer and Ohmic on the heavily doped substrate is reported. The resistivity of the ITO deposited separately on Si decreased from 1.83 10-3 Ω.cm as-deposited to 3.6 10-4 Ω.cm after 300 C anneal, with only minor reductions at higher temperatures (2.8 10-4 Ω.cm after 600 C anneals). The Schottky barrier height also decreased with annealing, from 0.98 eV in the as-deposited samples to 0.85 eV after 500 C annealing. The reverse breakdown voltage exhibited a negative temperature coefficient of -0.46 V.C-1 up to an annealing temperature of 400 C and degraded faster at higher temperatures. Transmission Electron Microscopy showed significant reaction at the ITO and Ga2O3 interface above 300 C, with a very degraded contact stack after annealing at 500 C.