INSTITUTE OF PHYSICS PUBLISHING PHYSICA SCRIPTA Phys. Scr. T126 (2006) 65–67 doi:10.1088/0031-8949/2006/T126/015 An AlGaN/GaN HEMT power switch employing a field plate and a floating gate Seung-Chul Lee, Min-Woo Ha, Jin-Cherl Her, Jiyong Lim, Kwang-Seok Seo and Min-Koo Han School of Electrical Engineering, Seoul National University, Shillim-dong, Seoul 151-742, Korea E-mail: nakupend@emlab.snu.ac.kr Received 21 August 2005 Accepted for publication 10 December 2005 Published 17 August 2006 Online at stacks.iop.org/PhysScr/T126/65 Abstract We have proposed and fabricated AlGaN/GaN high electron mobility transistors (HEMTs) which increase the gate-drain breakdown voltage by employing a floating gate and a field plate. Experimental results show that the breakdown voltage of the proposed devices was successfully increased compared with that of the devices which employ only the floating gate in our previous report. High breakdown voltage of 484 V is obtained while the breakdown voltage of the conventional devices is 250V. The leakage current is reduced considerably from 88 to 8.5 µA by employing the additional field plate. Measurement of dynamic characteristics shows that the proposed devices operate under high frequency inductive load switching without any current dispersion. PACS number: 81.05.Ea 1. Introduction AlGaN/GaN high electron mobility transistors (HEMTs) have attracted considerable attention for high power switch applications due to the wide band-gap properties of GaN [1]. GaN devices exhibit the high breakdown voltage characteristics due to the high field strength (>3 MV cm −1 ) compared with Si and GaAs devices [2]. In addition, very low on-resistance can also be obtained due to the two-dimensional electron gas (2DEG) of the AlGaN/GaN hetero-structure which exhibits high mobility and large carrier concentration [3–5]. AlGaN/GaN HEMT switches can operate at high temperature due to the wide band-gap properties of GaN. AlGaN/GaN HEMTs are suitable for high voltage power switches such as ignition circuits and inverter systems in hybrid vehicles due to these superior characteristics. Breakdown voltage and on-resistance are the important characteristics of power switches. Several methods have been reported to increase the breakdown voltage by reducing the electric field under the edge of the gate. It has been reported that the floating gate effectively reduces electric field concentration under the gate edge and suppresses the avalanche in GaAs MESFETs [6]. The floating gate may be an effective tool because it is formed simultaneously with the main gate so that the fabrication process is rather simple [7]. The field plate is also widely used in order to have high breakdown voltage in Si, SiC and GaN power devices [8, 9]. The floating gate and field plate are efficient methods which can reduce the electric field under the gate and improve the reverse characteristics. The purpose of this work is to report an AlGaN/GaN HEMT switch employing both a floating gate and a field plate in order to improve the reverse characteristics. The breakdown voltage of 484 V is obtained in the proposed HEMTs employing both the floating gate and the field plate while the breakdown voltage of the conventional HEMT, which only employs a floating gate, is 250V. The leakage current is reduced successfully from 88 to 8.5 µA by employing the additional field plate in the proposed HEMT. 2. Device structure and fabrication We have used an AlGaN/GaN HEMT epitaxial wafer which was grown on sapphire substrate by a MOCVD method. The 40 nm-thick AlN was grown on c-plane sapphire substrates as a nucleation layer, followed by a 3 µm-thick semi- insulating GaN layer. A 33-nm thick undoped AlGaN layer was deposited and a 5 nm-thick undoped GaN capping layer for a high breakdown voltage and a low leakage current was grown finally. The sheet charge concentration of 7.8 × 10 12 cm −2 and the electron mobility of 1500 cm 2 V −1 s −1 0031-8949/06/126065+03$30.00 © 2006 The Royal Swedish Academy of Sciences Printed in the UK 65