Microstructural properties of thermally stable Ti/W/Au ohmic contacts on n-type GaN

We have investigated the microstructural and electrical characteristics of Ti/W/Au ohmic contacts on n-type GaN (4.0 × 10¹⁸ cm⁻³) using Auger electron spectroscopy (AES) and transmission electron microscopy (TEM) after annealing at 900 °C. It is shown that the electrical properties are improved upon annealing at 900 °C for 1 min in nitrogen ambient. The 900 °C annealed contact produced a specific contact resistance of 8.4 × 10⁻⁶ Ω cm². It is further shown that the contact exhibits thermal stability during annealing at 900 °C. Based on the Auger electron microscopy and transmission electron microscopy studies, the formation of TiN layer results in an excess of N vacancies near the surface of the GaN layer, which could be the reason for the low-resistance of the Ti/W/Au contact.