Formation processes and properties of Schottky and ohmic contacts on n-type GaN for field effect transistor applications

Abstract

In view of applications to FETs, an attempt was made to characterize and optimize vacuum deposition-based formation processes of Schottky and ohmic contacts on n-type GaN. Detailed I–V and XPS measurements were made, changing surface treatments and metal species. Pre-deposition surface treatments were found to be crucial to obtain good electrical characteristics. Au Schottky contacts formed on warm NH 4OH treated surfaces showed nearly ideal thermionic-emission I–V characteristics with a highest Schottky barrier height of 1.03 eV. For ohmic contacts, Ti/Al contacts were investigated, using the circular transmission line model (TLM) method. Excellent ohmic characteristics with a minimum contact resistance of 5–8×10 −5 Ω cm −2 were obtained by annealing at 600°C for 1 min in N 2 atmosphere. Finally, narrow ring Au Schottky gates with Ti/Al ohmic electrodes were successfully fabricated, demonstrating applicability of the present contact formation processes for FET applications.