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.