Electrical characteristics of a-plane low-Mg-doped p-GaN Schottky contacts

摘要

Electrical characteristics of a variety of Schottky contacts formed with ten metal species on the a-plane of p-type low-Mg-doped GaN grown on r-plane sapphire substrates were studied. We found that while current-voltage characteristics obtained under voltage scanning show no memory effect in samples formed on a-plane samples on c-plane showed a substantial memory effects. We consider that the absence of memory effect in the a-plane p-GaN samples is originating from a smaller density of interfacial defect than that in the c-plane p-GaN samples. In internal photoemission spectra, we observed two linearly increasing portions suggesting two different Schottky barriers with different heights coexisting in a contact. A potential barrier corresponding to a linear increase locating at lower photon energy typically ranged between 1.6 and 2.5 eV; and that corresponding to another linear increase locating at higher energy ranged between 0.7 and 1.7. The barrier heights showed no relevance to metal work function. The a-plane GaN surface was found to reveal a lamellar structure with stripes along [0001] direction with a randomly oriented roughness. We thus speculate that contact barrier spatially varies according to the different crystal plane. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim