INSTITUTE OF PHYSICS PUBLISHING JOURNAL OF PHYSICS: CONDENSED MATTER J. Phys.: Condens. Matter 13 (2001) 7139–7157 PII: S0953-8984(01)25871-8 Gallium nitride based transistors H Xing 1 , S Keller 1 , Y-F Wu 2 , L McCarthy 1 , I P Smorchkova 1 , D Buttari 1 , R Coffie 1 , D S Green 1 , G Parish 1 , S Heikman 1 , L Shen 1 , N Zhang 1 , J J Xu 3 , B P Keller 2 , S P DenBaars 1 and U K Mishra 1 1 Electrical and Computer Engineering Department, University of California, Santa Barbara, CA 93106, USA 2 CREE Lighting Company, 340 Storke Road, Goleta, CA 93117, USA 3 Gtran, 1153 Lawrence Drive, Newbury Park, CA 91320, USA E-mail: hxing@ece.ucsb.edu Received 15 June 2001 Published 26 July 2001 Online at stacks.iop.org/JPhysCM/13/7139 Abstract An overview is presented of progress in GaN electronic devices along with recent results from work at UCSB. From 1995 to 2001, the power performance of AlGaN/GaN high electron mobility transistors (HEMT) improved from 1.1 to 11 W mm -1 , respectively. The disadvantage of the low thermal conductivity of the sapphire substrate was mitigated by flip-chip bonding onto AlN substrates, yielding large periphery devices with an output power of 7.6 W. A variety of HEMT amplifier circuits have been demonstrated. The first AlGaN/GaN heterojunction bipolar transistor (HBT) was demonstrated in 1998, with a current gain of about 3. By developing the technique of emitter regrowth, a current gain of 10 was achieved in both GaN BJTs and AlGaN/GaN HBTs. A common emitter current gain cutoff frequency of 2 GHz was measured. Critical issues involved in the growth of high quality AlGaN/(AlN)/GaN heterostructures and GaN:Mg by metal–organic chemical vapour deposition (MOCVD) and molecular beam epitaxy (MBE) and the device fabrication are discussed. 1. Introduction The gallium nitride materials system has established itself as extremely important for next generation opto-electronics by filling the void in the opto-electronic spectrum from the green to the ultra-violet. This has created new markets in green LED traffic signals, full colour outdoor displays and promises the next great advance in lighting since the fluorescent lamp. The promise of electronic applications is primarily in the area of sources and amplifiers for communications and low loss switches in power conditioning applications. (Al, Ga, In)N based semiconductors promise both to add on to present silicon, GaAs and InP based 0953-8984/01/327139+19$30.00 © 2001 IOP Publishing Ltd Printed in the UK 7139