The History of GaN electronics: A perspective

The development of Gallium Nitride HEMTs has been an amazing ride since its invention by Khan et al. in 1993. The first demonstration of microwave power by Wu et al. in 1996 was another significant milestone. The measured power of 1.1W/mm was higher than most GaAs devices at that time and showed the immediate promise of the AlGaN/GaN HEMT as a power source. Doped AlGaN/GaN devices without passivation showed power density of up to 4W/mm but the identification of dispersion being the cause of limited output power and the application of SiN passivation by Green et al. and Wu et al. (1999/2000) broke through this barrier and led to power densities greater than 6W/mm even on undoped HEMTs. Next the use of AlN spacers to enhance channel mobility by Shen et al. (2001) and the incorporation of gate connected field plates by Chini et al. (2004) enabled power densities (>10W/mm) with high efficiency. The optimization of both gate and source connected field plates led to an astonishing 40W/mm power density by Wu et al. in (2006). Today, thanks to the efforts of several companies such as Wolfspeed, SEDI, Qorvo and NXP amongst others, the 5G base station market is being enabled and served by AlGaN/GaN HEMTs. The development of AlGaN/HEMTs and its transition to DoD Systems was highlighted in 2018 at the DARPA D60 as one of the major achievements at DARPA. More recently the development of N-polar GaN at UC Santa Barbara has led to remarkable mm-wave performance of 8.8W/mm at 94GHz which demonstrates that the AlGaN/GaN HEMT roadmap shows tremendous promise for the next decade and beyond. The ONR, which has provided sustained funding of GaN since the 1990s, highlighted GaN electronics’ successes during its 75th anniversary celebrations.