Analysis of leakage current mechanisms in Schottky contacts to GaN and Al0.25Ga0.75N∕GaN grown by molecular-beam epitaxy

Abstract

Temperature-dependent current-voltage measurements combined with conductive atomic force microscopy and analytical modeling have been used to assess possible mechanisms of reverse-bias leakage current flow in Schottky diodes fabricated from GaN and Al0.25Ga0.75N∕GaN structures grown by molecular-beam epitaxy. Below 150K, leakage current is nearly independent of temperature, indicating that conduction is dominated by tunneling transport. At higher temperatures, leakage current in both GaN and Al0.25Ga0.75N∕GaN diode structures is well described by a Frenkel-Poole emission model. Based on the inferred emission barrier heights and the observation that room-temperature leakage current is dominated by the presence of highly conductive dislocations, it is suggested that the key carrier transport process is emission of electrons from a trap state near the metal-semiconductor interface into a continuum of states associated with each conductive dislocation. In this model for leakage current flow, the emission barrier heights measured for the GaN and Al0.25Ga0.75N∕GaN diode structures indicate that the conductive dislocation states are aligned in energy between GaN and Al0.25Ga0.75N.