Investigation of Ti/Au and Ti2N/Ti/Au ohmic contacts to n-GaN films
Characteristics of Ti/Au and Ti2N/Ti/Au ohmic contacts on n-type GaN films were investigated in detail, before and after the thermal annealing. As-deposited GaN/Ti/Au contacts showed ohmic properties with low resistivity, ~3.7 × 10−5 Ω cm2, but showed rectifying properties after heat treated at temperatures higher than 500 °C. Formation of new phases at the GaN/Ti interfaces, such as Ga3Ti5, Ga4Ti5, and TiN, was observed in the case of 700 °C annealed samples, which were proposed to be responsible for the high-temperature degradation. As-deposited GaN/Ti2N/Ti/Au contact was also ohmic, with ~8.2 × 10−5 Ω cm2 resistivity. Heat treated samples showed lower resistivity, ~2.2 × 10−5 Ω cm2 for the 700 °C and ~6.2 × 10−5 Ω cm2 for the 800 °C, suggesting that the Ti2N buffer layer prevented or minimized interfacial reaction between GaN and Ti, resulting in much better thermal stability.