Properties of Pt Schottky contacts on modulation-doped AlxGa1-xN/GaN heterostructures

Forward and reverse current-voltage characteristics of the Pt Schottky contacts on modulation-doped Al_0.22Ga_0.78N/GaN heterostructures were investigated. The barrier height of 0.94 eV and the ideality factor of 1.4 were obtained for the sample with the Si-doping level of 7.5 × 10¹⁷ cm^-3 in the top Al_0.22G_0.78N barrier layer. The barrier height is lower and the ideality factor is larger for the samples with higher Si-doping level in the barrier. The reverse current mechanism are also different for the samples with different doping level of the Al_0.22Ga_0.78N barrier. It is suggested that the interfacial properties are crucial to the current-voltage characteristics of the samples. Capacitance-frequency measurement indicates that the density of the metal-semiconductor interfacial states are higher for the samples with higher Si-doping level in the barrier. It is thought that the chemical properties of the Al_0.22Ga_0.78N surface are influenced by the Si-doping level of Al_0.22Ga_0.78N, resulting in the difference in Pt/Al_0.22Ga_0.73N interfacial properties.