Mechanism of anomalous current transport in n-type GaN Schottky contacts

Abstract

Temperature T dependences of the current–voltage (I–V) characteristics of Ni and Pt/n-GaN Schottky contacts were measured in detail, and the results were analyzed from various viewpoints. Large deviations from the thermionic emission transport were observed in the I–V–T behavior with anomalously large reverse leakage currents. Forward characteristics could be fitted into the classical thermionic-field emission (TFE)/field emission (FE) model. However, an unusually high doping density had to be assumed, and the reverse characteristics were far away from measured data. A new thin surface barrier (TSB) model was proposed in which the width of the Schottky barrier is reduced due to the presence of unintentional surface donors. Analysis of TFE/TE process through the TSB region has led to sets of I–V–T curves that reproduce almost perfectly the observed forward and reverse I–V–T behavior with correct orders of magnitude of currents. Deep donors related to nitrogen vacancy are suggested to be the origin of surface donors producing TSBs.