Reduction of Ohmic Contact Resistivity on p-Type GaN by Surface Treatment

The contact resistivity of transparent Pt contact on p-type GaN was drastically decreased by four orders of magnitude through the surface treatments in sequence using aqua regia and (NH4)2Sx solution. The surface oxide on p-type GaN formed during epitaxial growth was removed in the boiling aqua regia, and the formation of native oxide on the oxide-free surface during air exposure prior to metal deposition was suppressed by the (NH4)2Sx treatment. This suggests that the reduction of contact resistivity is due to direct contact of Pt on the clean surface of p-type GaN, via shift of the Fermi level to a energy level of acceptors near the valence band, resulting in the reduction of barrier height for holes at the interface of Pt/p-type GaN.