The role of cleaning conditions and epitaxial layer structure on reliability of Sc 2 O 3 and MgO passivation on AlGaN/GaN HEMTS B.Luo a, * ,R.M.Mehandru a ,JihyunKim a ,F.Ren a ,B.P.Gila b ,A.H.Onstine b , C.R. Abernathy b , S.J. Pearton b , R.C. Fitch c , J. Gillespie c , R. Dellmer c , T. Jenkins c , J. Sewell c , D. Via c , A. Crespo c a Department of Chemical Engineering, University of Florida, Gainesville, FL 32611, USA b Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611, USA c Air Force Research Laboratory, Sensors Directorate, Wright-Patterson AFB, OH 45433-7322, USA Received 17 January 2002; received in revised form 3 April 2002; accepted 29 April 2002 Abstract The effect of layer structure (GaN versus AlGaN cap) and cleaning procedure prior to Sc 2 O 3 or MgO deposition at 100 °C were examined for their effects on the long-term bias-stress stability of AlGaN/GaN high electron mobility transistors(HEMTs).Surfacecleaningbyitselfwasnotsufficienttopreventcurrentcollapseinthedevices.Theforward andreversegateleakagecurrentsweredecreasedundermostconditionsupondepositionoftheoxidepassivationlayers. After 13 h of bias-stressing, the MgO-passivated HEMTs retain P 90% their initial drain–source current. The Sc 2 O 3 - passivated devices retained 80% recovery of the current under the same conditions. Ó 2002 Published by Elsevier Science Ltd. Keywords: GaN HEMT, Current dispersion; Gate lag measurement; Oxide passivation film; Bias-Stressing test 1. Introduction Remarkable progress have been made in recent times in developing insulator-GaN heterostructures with a low density of interfacial states [1]. This has led to the recent demonstration of inversion behavior in MgO/p-GaN gated devices [2], which is a critical first step towards development of enhancement-mode GaN MOSFETs. Both MgO and Sc 2 O 3 have been found to have a low interfacial state density ( 6 3  10 11 cm 2 eV 1 at 25 °C) on GaN when deposited under molecular beam epitaxy (MBE) conditions [3,4]. These materials may also be employed as surface passivation layers on AlGaN/GaN high electron mobility transistors (HEMTs) in order to reduce the effects of current degradation and transcon- ductance dispersion that result from surface traps be- tween the gate and drain region of the device [5,6]. The oxides are found to provide more effective passivation than other reported films used for the same purpose, such as SiN x [7–13]. The absence of hydrogen in the oxides also makes them attractive candidates for long- term stable passivation of the HEMTs. While some initial results have shown excellent long-term stability (>5 months for Sc 2 O 3 in AlGaN/GaN HEMTs) under un-biased conditions, there is a need to investigate the reliability under bias-stress testing conditions. In this paper, we report on some initial experiments onSc 2 O 3 and MgO passivation of HEMTs after biasing for periods up to 13 h. The critical issues for achieving acceptable stability of the passivation are reported. * Corresponding author. Tel.: +1-352-392-4727; fax: +1-352- 392-9513. 0038-1101/02/$ - see front matter Ó 2002 Published by Elsevier Science Ltd. PII:S0038-1101(02)00229-0 Solid-State Electronics 46 (2002) 2185–2190 www.elsevier.com/locate/sse