Formation of Ti/Al ohmic contacts on Si-doped GaN epilayers by low temperature annealing

Abstract

Ohmic contacts have been fabricated on Si-doped GaN using Ti/Al by low temperature annealing at 500°C. A contact resistivity of 8.6 × 10-6 ohm cm2 was obtained for n-GaN samples doped to 3.67 × 1018 cm-3. Secondary ion mass spectrometry (SIMS) analysis showed that Al diffused through the Ti layer after annealing. Furthermore, energy dispersive x-ray spectroscopy (EDS) analysis showed that reaction products of Al, Ti, Ga and N were present at the interface. Hence, a complex ternary or quaternary nitride as a possible low barrier height material to n-GaN may have resulted in good ohmic contact. Photoluminescence (PL) showed that there was no degradation in the epilayer quality of the film after annealing at 500°C for 25 minutes.