Electrical and microstructural properties of low‐resistance Ti/Re/Au ohmic contacts to n‐type GaN

The microstructural and electrical properties of Ti/Re/Au (10 nm/10 nm/50 nm) ohmic contacts to moderately doped n‐type GaN (4.0 × 10 18 cm –3 ) have been investigated by current–voltage ( I – V ), Auger electron microscopy (AES) and transmission electron microscopy (TEM). The electrical characteristics of as‐deposited and annealing at temperatures below 800 °C samples exhibit non‐linear behaviour. However, the sample showed ohmic behaviour when the contact is annealed at 900 °C for 1 min in nitrogen ambient. The Ti/Re/Au contacts give specific contact resistance as low as 8.6 × 10 –6 Ω cm 2 after annealing at 900 °C. It is shown that the surface of the as‐deposited contact is fairly smooth and slightly degraded when the contact is annealed at 900 °C. The Ti/Re/Au ohmic contact showed good edge acuity after annealing at 900 °C for 1 min. Based on the Auger electron microscopy and transmission electron microscopy results, possible ohmic formation mechanisms for the Ti/Re/Au contacts to the n‐type GaN are described and discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)