Thermal stability of TaN Schottky contacts on n-GaN

The thermal stability and electrical characteristics of tantalum-nitrogen alloy Schottky contacts on n-GaN were investigated. Non-stoichiometric delta-phase (40 atomic percent nitrogen) tantalum nitride contacts exhibited good electrical properties up to an annealing temperature of 600degreesC. However, they degrade rapidly above this temperature due to outward diffusion of Ga and presumably nitrogen into the delta-phase tantalum nitride. It is surmised that excess Ta reacts with N at the GaN surface, freeing Ga which then diffuses into the TaN layer. Stoichiometric TaN Schottky contacts were stable at temperatures as high as 800degreesC and had far superior electrical performance. This stems from the thermodynamic stability of the stoichiometric TaN/GaN interface. delta-phase TaN had IN and C-V barrier heights of 0.55 eV and 0.8 eV respectively. On the other hand, TaN had an I-V barrier height near 0.7 eV and a C-V barrier height near 1.2 eV. The ideality factors for both delta-phase TaN and TaN were above 1.8 at all annealing temperatures, suggesting tunneling contributes significantly to current transport. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.