Monolithic Integration of Enhancement- and Depletion-Mode AlN/GaN/AlGaN DHFETs by Selective MBE Regrowth

We have achieved the monolithic integration of two Ill-nitride device structures through the use of etching and re growth by molecular beam epitaxy (MBE). Using this regrowth technique, we integrated enhancement-mode (E-mode) and depletion-mode (D-mode) AIN/GaN/AlGaN double-heterojunction field-effect transistors (DHFETs) on a single SiC substrate, wherein the E-mode devices had a 2-nm-thick AlN barrier layer and the D-mode devices had a 3.5-nm-thick AlN barrier layer. The direct-current and radio-frequency (RF) performance of the resulting DHFETs was equivalent to devices fabricated using our baseline process with a normal MBE growth. D-mode devices with a gate length of 150 nm had a threshold voltage Vth of -0.10 V, a peak transconductance gm value of 640 mS/mm, and current gain and power-gain cutoff frequencies fT and fmax of 82 and 210 GHz, respectively. E-mode devices on the same wafer with the same dimensions had a Vth value of +0.24 V, a peak gm value of 525 mS/mm, and fT and fmax values of 50 and 150 GHz, respectively. The application of this regrowth technique is not, in any way, limited to the integration of E- and D-mode devices, and this method greatly expands the design possibilities of RF and power switching circuits in the nitride material system.