Anisotropic electrical conductivity of surface-roughened semipolar GaN films by photochemical etching

We studied the anisotropy of electrical conductivity in surface-roughened semipolar GaN (s-GaN) films. Highly crystalline s-GaN films were obtained using asymmetric lateral epitaxy on oxide-patterned m-plane sapphire substrates. The in-plane structural anisotropy of the s-GaN films was confirmed by anisotropic peak broadening in X-ray rocking curves (XRC) with the in-beam orientations. The XRC full-width at half maximum (FWHM) values were measured to be 454 and 615 arcsec along the GaN and GaN directions, respectively. The s-GaN surface was roughened using photo-chemical etching, and the electrical anisotropy was then investigated as a function of azimuth angles with the transmission line method. The Ohmic contact properties on the roughened s-GaN surface did not depend on the azimuth angle or annealing temperatures between 750 and 950 °C. The sheet resistances parallel to the GaN direction on roughened s-GaN were found to be approximately half of the resistance parallel to the GaN direction, showing that anisotropic electrical conductivity is maintained for surface-roughened s-GaN due to charged carrier scattering induced by basal-plane stacking faults.