Gallium nitride based transistors

An overview is presented of progress in GaN electronic devices along with r ecent results from work at UCSB. From 1995 to 2001, the power performance o f 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 AIN subs trates, yielding large periphery devices with an output power of 7.6 W. A v ariety of HEMT amplifier circuits have been demonstrated. The first AlGaN/G aN 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 co mmon emitter current gain cutoff frequency of 2 GHz was measured. Critical issues involved in the growth of high quality AlGaN/(AlN)/GaN heterostructu res and GaN:Mg by metal-organic chemical vapour deposition (MOCVD) and mole cular beam epitaxy (MBE) and the device fabrication are discussed.