Low-resistance Cr/Al Ohmic contacts to N-polar n-type GaN for high-performance vertical light-emitting diodes

Abstract

We investigated the electrical properties of Cr(30 nm)/Al(200 nm) contacts to N-polar n-type GaN for high-performance vertical light-emitting diodes and compare them with those of Ti(30 nm)/Al(200 nm) contacts. Before annealing, both the samples show ohmic behaviors with a contact resistivity of 1.9-2.3 x 10(-4) Omega cm(2). Upon annealing at 250 degrees C for 1 min in N-2 ambient, the Ti/Al contacts become non-ohmic, while the Cr/Al contacts remain ohmic with a contact resistivity of 1.4 x 10(-3) Omega cm(2). Based on X-ray photoemission spectroscopy and secondary ion mass spectrometry results, ohmic formation and degradation mechanisms are briefly described and discussed. (C) 2011 Elsevier B. V. All rights reserved.