Ohmic Contact Properties of Photo-Chemically Etched Nonpolar a-Plane (11-20) GaN Films

Abstract

Nonpolar a-plane (11-20) 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 {10-10} facets. The properties of Ti/Al/Ni/Au Ohmic contact on surface-textured a-GaN ?lms were studied with transmission line method patterns aligned along the speci?c crystal orientations. The minimum speci?c contact resistance of 9.97×10?5 cm2 was achieved along the c-axis on the etched GaN surface at the annealing temperature of 750?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 ?lm could be explained by more dominant effect of surface roughness scattering.