Ohmic Contact Properties of Photo-Chemically Etched Nonpolar A-Plane GaN Films

Nonpolar a-plane (11 (2) over bar0) GaN (a-GaN) was photo-chemically etched under ultraviolet illumination using alkali KOH solution, and the Ohmic contact properties on the etched a-GaN epitaxial layer were investigated. After photo-chemical etching, the striated surface morphology along the c-axis [0001] direction was obtained having triangular prisms consisting of m-plane {10 (1) over bar0} facets. The properties of Ti/Al/Ni/Au Ohmic contact on surface-textured a-GaN films were studied with transmission line method patterns aligned along the specific crystal orientations. The minimum specific contact resistance of 9.97 x 10(-5) Omega.cm(2) was achieved along the c-axis on the etched GaN surface at the annealing temperature of 750 degrees C. The etched a-GaN showed higher electrical conductivity along the c-axis than along m-axis. This anisotropic behavior is in contrast to that of the unetched a-GaN where carrier scattering by basal plane stacking faults in the direction perpendicular to the c-axis is a major factor in determining opposite anisotropic conductivity. The higher conductivity along the c-axis of the etched a-GaN film could be explained by more dominant effect of surface roughness scattering. (c) The Author(s) 2017. Published by ECS. All rights reserved.