Recess-free enhancement-mode AlGaN/GaN RF HEMTs on Si substrate

Enhancement-mode (E-mode) GaN-on-Si radio-frequency (RF) high-electron-mobility transistors (HEMTs) were fabricated on an ultrathin-barrier (UTB) AlGaN (<6 nm)/GaN heterostructure featuring a naturally depleted 2-D electron gas (2DEG) channel. The fabricated E-mode HEMTs exhibit a relatively high threshold voltage ( V TH ) of +1.1 V with good uniformity. A maximum current/power gain cut-off frequency ( f T / f MAX ) of 31.3/99.6 GHz with a power added efficiency (PAE) of 52.47% and an output power density ( P out ) of 1.0 W/mm at 3.5 GHz were achieved on the fabricated E-mode HEMTs with 1- µ m gate and Au-free ohmic contact.