Enhancement-mode Al0.85Ga0.15N/Al0.7Ga0.3N high electron mobility transistor with fluorine treatment

Enhancement-mode Al0.7Ga0.3N-channel high electron mobility transistors (HEMTs) were achieved through a combination of recessed etching and fluorine ion deposition to shift the threshold voltage (V-TH) relative to depletion-mode devices by +5.6V to V-TH = +0.5 V. Accounting for the threshold voltage shift (Delta V-TH), current densities of approximately 30 to 35mA/mm and transconductance values of 13 mS/mm were achieved for both the control and enhancement mode devices at gate biases of 1V and 6.6 V, respectively. Little hysteresis was observed for all devices, with voltage offsets of 20 mV at drain currents of 1.0 x 10(-3) mA/mm. Enhancement-mode devices exhibited slightly higher turn-on voltages (+0.38 V) for forward bias gate currents. Piecewise evaluation of a threshold voltage model indicated a DVTH of +3.3V due to a gate recess etching of 12 nm and an additional +2.3V shift due to fluorine ions near the AlGaN surface. Published under license by AIP Publishing.