Ti/Al/Pt/Au and Al ohmic contacts on Si-substrated GaN

Abstract

Al and Ti/Al/Pt/Au ohmic contacts on GaN epitaxial layers were studied. The epilayers were grown on Si (111) substrates by low-pressure metalorganic chemical vapor deposition. Al/GaN contacts achieved a minimum contact resistivity of 7.5×10−3 Ω cm2 after annealing in N2 ambient at 450 °C for 3 min. Further annealing degraded the contacts. Ti/Al/Pt/Au and GaN contacts achieved a minimum contact resistivity of 8.4×10−5 Ω cm2 after annealing in N2 at 650 °C for 20 s. The Ti/Al/Pt/Au contacts on GaN showed a better thermal stability than Al/GaN contacts. After annealing at 600 °C for 30 min. they were still ohmic contacts. The mechanisms for ohmic contact formation of Ti/Al/Pt/Au contacts were also analyzed.