High temperature Ohmic contacts to p‐type GaN for use in light emitting applications

Abstract

Achieving low resistance contacts to p‐type Gallium Nitride is a critical requirement for the fabrication of reliable AlGaN/InGaN laser diodes and nitride‐based light‐emitting diodes (LEDs). Three separate groups of materials are examined. The first is a family of borides, including W2B, W2B5, CrB2, TiB2, and ZrB2; the second is a group of nitrides, TaN, TiN, and ZrN; and the third is the refractory metal Ir. Using these materials both directly on the surface of p‐GaN as well as a diffusion barrier for Ni/Au‐based Ohmic contacts, specific contact resistances as low as ∼1x10–4 Ω.cm2 have been achieved. In addition, the boride and iridium based contacts display superior aging characteristics with minimal degradation of the contact resistance and of the turn on voltage of light emitting diodes after extended periods at 350 °C. The reasons for the discrepancies in performance of different materials is examined through the use of IV curves as well as Auger Electron Spectroscopy (AES) depth profiles. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)