Temperature dependent forward current-voltage characteristics of Ni/Au Schottky contacts on AlGaN/GaN heterostructures described by a two diodes model

This paper reports on the temperature dependence of Ni/Au Schottky contacts on AlGaN/GaN heterostructures. The electrical properties of the Schottky barrier were monitored by means of forward current-voltage (I–V) measurements, while capacitance-voltage measurements were used to determine the properties of the two dimensional electron gas. The forward I–V characteristics of Schottky diodes revealed a strong deviation from the ideal behavior, which could not be explained by a standard thermionic emission model. Thus, the Ni/AlGaN/GaN system has been described by a “two diode model,” considering the presence of a second barrier height at the AlGaN/GaN heterojunction. Following this approach, the anomalous I–V curves could be explained and the value of the flat-band barrier height (at zero-electric field) could be correctly determined, thus resulting in good agreement with literature data based on photoemission measurements.