Low resistance and thermally stable Ti/Al-based Ohmic contacts to N-facen-GaN for vertical light-emitting diodes by using Ti(Ga) solid solution and TiN layers

Abstract

The authors report on the formation of highly reliable Ti/Al-based ohmic contacts to N-face n-GaN for high-performance vertical light-emitting diodes by using Ti(Ga) solid solution and TiN layers. The Ti(Ga) solid solution layer is used to minimize the outdiffusion of Ga atoms from the n-GaN surface region. Unlike the Ti/Al contacts, the Ti(Ga)/Ti/Al and Ti(Ga)/TiN/Al samples exhibit ohmic behavior with contact resistivities of 3.9 - 4.8 x 10(-4) Omega cm(2) after annealing at 250 degrees C. It was further shown that unlike the Ti(Ga)/TiN/Al samples, the Ti/Al and the Ti(Ga)/Ti/Al samples are largely electrically degraded when annealed at 300 degrees C in an oven. Based on x-ray photoemission spectroscopy and secondary ion mass spectrometry results, ohmic formation and degradation mechanisms are briefly described and discussed. (C) 2012 American Vacuum Society. [DOI: 10.1116/1.3678490]