Electronic Transport and Schottky Barrier Heights of Ni/Au Contacts on n-Type GaN Surface with and without a Thin Native Oxide Layer

Abstract

Effects of a thin native oxide layer on Au/Ni/n-type GaN Schottky diodes were investigated in this study. The tunneling current was induced in the presence of native oxides on the GaN surface, making the thermionic emission (TE) theory inapplicable in this case. We find that the value of the barrier height (BH) calculated using the thermionic field emission (TFE) model is similar to that obtained by capacitance–voltage characteristics. This suggested that the discrepancy between BH according to the TFE and TE model for Au/Ni/n-type GaN Schottky diodes could be attributed to the presence of a native oxide layer at the Ni/n-type GaN interface and oxygen-induced and nitrogen-vacancy-related states on the GaN surfaces. Further, the characteristics of Schottky diodes improved when the n-type GaN was treated with (NH4)2Sx solution, an effective agent for removing native oxides and reducing surface states.