AlGaN/GaN HEMTs grown by Molecular Beam Epitaxy on sapphire, 6H-SiC, and HVPE-GaN templates

We report on a systematic study of the growth of AlGaN/GaN HEMT structures by plasma-assisted Molecular Beam Epitaxy (MBE) on different substrates, including sapphire, 6H-SiC, and GaN templates prepared by Hydride Vapour Phase Epitaxy (HVPE). We obtained record low-temperature mobilities of 75,000 cm ²/Vs from HEMT structures with low sheet charge (∼10 ¹² cm^-2) grown on HVPE GaN templates, and demonstrated functioning AlGaN/GaN HEMT devices on HVPE templates grown by MBE for the first time. HEMT devices of equal geometries were fabricated on all three substrates, allowing for a direct comparison between the different substrate technologies for GaN MBE growth. Our best devices on semi-insulating 6H-SiC substrates delivered a saturated power density of 6.2 W/mm at 2 GHz, and 4.9 W/mm at 7 GHz in continuous wave class A mode. A record drain current density of 1798 mA/mm was recorded from a submicron HEMT on SiC.