Passivation of Surface and Interface States in AlGaN/GaN HEMT Structures by Annealing HYEONGNAM KIM, 1 MICHAEL L. SCHUETTE, 1 JAESUN LEE, 1 WU LU, 1,3 and JAMES C. MABON 2 1.—Department of Electrical and Computer Engineering, The Ohio State University, Columbus, OH 43210,USA. 2.—Center for Microanalysis of Materials,Frederick Seitz Materials Research Laboratory, 104 S. Goodwin Avenue, Urbana, IL 61801, USA. 3.—e-mail: lu@ece.osu.edu The Ni/AlGaN interfaces in AlGaN/GaN Schottky diodes were investigated to explore the physical origin of post-annealing effects using electron beam in- duced current (EBIC), current–voltage (I–V) characteristics, and X-ray pho- toelectron spectroscopy (XPS).The EBIC images of the annealed diodes showed that the post-annealing process reduces electrically active states at the Schottky metal/AlGaN interfaces, leading to improvement of diode per- formance, for example a decrease in reverse leakage current and an increase in Schottky barrier heights. Pulsed I–V characteristics indicate the Fermi level is up-shifted after annealing, resulting in a larger sheet carrier density at the AlGaN/GaN interface. Unintentional oxidation of the free AlGaN sur- face during the post-annealing process, revealed by XPS analysis,may pre- vent electron trapping near the drain-side of the gate edges. We suggest that the post-annealing process under an optimized conditions can be an effective way of passivating AlGaN/GaN heterojunction field-effect transistors. Key words: AlGaN/GaN HEMT, post-gate annealing, surface/interface states, passivation INTRODUCTION Control of surface states is an important issue in AlGaN/GaN high-electron-mobility transistors (HEMTs) for high-power, high-speed, and high- temperature applications. 1–5 For high-performance AlGaN/GaN HEMTs many efforts have been made to suppress RF current dispersion and thermal/ electrical stress-induced degradation, or/and to improve the breakdown voltage performance, which are directly related to the electron trapping behav- ior because of surface states in AlGaN/GaN hetero- structures. There have been many reports about the origin of surface states in GaN-based materials, for example threading dislocations (TDs), nitrogen vacancies (V N ), and oxygen impurities. 6–9 TDs have been mostly considered to be negatively charged, 6,7 although positively charged states at TDs have also been reported. 10 Hsu et al. suggested that the elec- trical behavior of dislocations depends on growth conditions and screw and mixed dislocations intro- duce excess reverse leakage current in GaN Schotty diodes. 11 V N and oxygen impurities as shallow sur- face donors have also been reported to cause gate leakage current. 8,9 Effects on device performance have been investigated for various techniques used to engineer electrically active surface states—surface passivation, dielectric layer inser- tion, surface treatments with chemicals or plasma, and post-gate-annealing. 1–5,12–18 We have reported that thermal annealing after Schottky gate forma- tion can be used to engineer surface/interface states in AlGaN/GaN HEMTs to improve device RF power performance; it has been suggested this is related to the change of trap activities near the metal/AlGaN interface. 5 Reported annealing effects on Schottky contacts on AlGaN/GaN heterostructures include reduc- tion of reverse leakage currentand improvement of Schottky barrier height and breakdown (Received August 4, 2006; accepted April 18, 2007; published online July 24, 2007) Journal of ELECTRONIC MATERIALS, Vol. 36, No. 9, 2007 Regular Issue Paper DOI: 10.1007/s11664-007-0189-2 2007 TMS 1149