Formation of low resistance Ti/Al-based ohmic contacts on (11-22) semipolar n-type GaN

Abstract

The electrical properties of Ti/Al-based ohmic contacts to (0001) c-plane and (11-22) semipolar n-type GaN were investigated as a function of annealing temperature. The electrical properties of both c-plane Ti/Al/Au and semi-polar Ti/(Ta)/Al/Au contacts became improved upon annealing at 600 degrees C for 1 min. The specific contact resistances of the 600 degrees C-annealed c-plane Ti/Al/Au, semi-polar Ti/Al/Au, and semipolar Ti/Ta/Al/Au contacts were 3.2 x 10(-4), 1.5 x 10(-4), and 4.8 x 10(-5) Omega cm(2), respectively. The X-ray photoemission spectroscopy (XPS) results showed that the Ga 2p core level for the c-plane samples experienced a smaller shift toward the conduction band than that for the semipolar samples. The XPS depth profile results exhibited that the semipolar samples contained more interfacial oxygen than the c-plane samples. Oxygen was present in the form of Al-oxide at the interface region, but as oxygen atoms in the GaN surface region. On the basis of the electrical and XPS results, the annealing-induced improvement of the electrical properties was described in terms of the formation of donor-like defects. (C) 2015 Elsevier B.V. All rights reserved.