Transient response of highly doped thin channel GaN metal–semiconductor and metal-oxide–semiconductor field effect transistors N. Pala a, * , S.L. Rumyantsev a,1 , M.S. Shur a , X. Hu b , A. Tarakji b , R. Gaska b , M. Asif Khan c , G. Simin c , J. Yang c a Department of Electrical, Computer, and Systems Engineering and Center for Integrated Electronics and Electronics Manufacturing, CII 9017, Rensselaer Polytechnic Institute, Troy, NY 12180-3590, USA b Sensor Electronic Technology, Inc., 21 Cavalier Way, Latham, NY 12110, USA c Department of Electrical and Computer Engineering, University of South Carolina, Columbia, SC 29208, USA Received 22 August 2001; accepted 17 September 2001 Abstract The transient characteristics of GaN highly doped thin channel metal–semiconductor and metal-oxide–semicon- ductor field effect transistors were investigated by switching the transistors from the OFF to the ON state. Transient gated transmission line model measurements showed that the channel resistance under the gate remains constant and the current collapse effects are linked to the transient variations of the series source–gate and gate–drain resistances, similar to what was previously reported for GaN/AlGaN heterostructure field effect transistors. The transient tem- perature measurements revealed that trapping processes responsible for the transient behavior cannot be described by the activation mechanism. Ó 2002 Published by Elsevier Science Ltd. 1. Introduction A recent report on GaN-based highly doped thin channel metal–semiconductor field effect transistors (HD-MESFETs) showed that their performance can compete with that of AlGaN/GaN heterostructure field effect transistors (HFETs), whereas these devices have the advantage of a simpler epilayer structure [1]. One of the problems observed in GaN-based tran- sistors is the current collapse (or current slump). As a result, the output RF power, even measured under pulse conditions,isalwayssmallerthanthatexpectedfromthe DC current–voltage characteristics [2]. Although the fundamental cause for the current col- lapse is not completely understood, a number of expla- nations have been proposed. For HFETs, traps at the surfaceand/orintheAlGaNbarrierlayerweresuggested to be responsible for current collapse [3,4]. In GaN MESFETs, electron trapping at the buffer layer beneath the channel was suggested as a relevant mechanism [5,6]. Later, experiments showed that the traps can also be locatedinand/oronthesurfaceofGaNchannellayer[7]. Recently, Simin et al. proposed a current collapse model based on piezoelectric charge variations in the source– gate and gate–drain regions due to the gate bias induced non-uniform strain in AlGaN barrier layer [8]. In this article, we present the experimental results on the transient characteristics of GaN HD-MESFETs and highly doped thin channel metal-oxide–semiconductor field effect transistors (HD-MOSFETs). Our results show that these devices do exhibit the current collapse. Although many features of this collapse are similar to those in HFETs, the results discussed below also reveal some important differences. Solid-State Electronics 46 (2002) 711–714 * Corresponding author. Tel.: +1-518-276-6405; fax: +1-518- 276-2990. E-mail address: palan@rpi.edu (N. Pala). 1 On leave from the Ioffe Institute of Russian Academy of Sciences, 194021 St-Petersburg, Russia. 0038-1101/02/$ - see front matter Ó 2002 Published by Elsevier Science Ltd. PII:S0038-1101(01)00302-1