Surface Fermi level pinning and carrier transport of indium-tin-oxide Ohmic contact to p-type GaN

The carrier transport mechanism of indium-tin-oxide (ITO) Ohmic contact to p-type GaN was investigated. The thermally annealed ITO contact to p-GaN produced a low specific contact resistance of 8.1 × 10 ^-3 Ω cm ², due to the low effective barrier height of 0.11 eV, for which the carriers must overcome to flow from p-GaN to the metals via hopping conduction through deep-level defect states. The surface Fermi level of a highly Mg-doped p-GaN surface was also found to pin near the midgap states, i.e., ∼0.6 of bandgap above valence band, which are caused by deep-level defect states.