Ohmic Contact Properties of Non-Polar (10(1)over-bar0) m-Plane Bulk GaN Crystals

Abstract

We report on the properties of Ti/Al/Ni/Au Ohmic contacts and their electrical anisotropy on undoped non-polar m-plane (10 (1) over bar0) GaN (m-GaN) bulk crystals. High-resolution X-ray rocking curve (XRC) analysis confirmed the high crystallinity of the m-GaN single crystal. Peak widths of the XRC were measured to be 50 and 128 arcsec along the [11 (2) over bar0]GaN and [0001](GaN) directions, respectively. A minimum specific contact resistance of similar to 1.7 x 10(-4) Omega.cm(2) was obtained after annealing at 850 degrees C on transmission line method patterns along the [1 (1) over bar 00](GaN) direction. Sheet resistances parallel to the [0001](GaN) direction were found to be approximately 2 to 3 times higher than those parallel to the [11 (2) over bar0](GaN) direction, indicating significant electrical anisotropy. In addition, sheet resistance increased approximately linearly with increasing azimuth angle for all annealing temperatures. The basal-plane stacking fault-induced carrier scattering is thought to be primarily responsible for the anisotropic conductivity in the case of m-GaN bulk crystals.