Nitride-based Ohmic and Schottky Contacts to GaN

Abstract

Ohmic and Schottky contact formation on n-GaN using ZrN, TiN and TaN-based metallization schemes was studied. For GaN layers with an electron concentration of ~3×1017 cm-3, the minimum specific contact resistance achieved is 6x10-5 Ω cm2 for Ti/Al/TiN/Ti/Au after annealing at 800{degree sign}C. The specific contact resistance was found to strongly depend on the doping level, suggesting that tunneling is the dominant mechanism of current flow. TiN/Pt/Au and ZrN/Pt/Au metallurgies exhibited rectifying behavior up to 900{degree sign}C anneal, the maximum barrier height being ~0.85 eV for ZrN/Pt/Au after 750{degree sign}C anneal. While this value is comparable to that of standard Ni/Au and Pt/Au rectifying contacts on the same n-GaN layer, the nitride-based metallization schemes show considerable smoother surface morphologies, even after annealing in the 750-900{degree sign}C range.