50-nm E-mode In 0.7 Ga 0.3 As PHEMTs on 100-mm InP substrate with f max > 1 THz

We have demonstrated 50-nm enhancement-mode (E-mode) In 0.7 Ga 0.3 As PHEMTs with f max in excess of 1 THz. The devices feature a Pt gate sinking process to effectively thin down the In 0.52 Al 0.48 As barrier layer, together with a two-step recess process. The fabricated device with L g = 50-nm exhibits V T = 0.1 V, g m,max = 1.75 mS/µm, f T = 465 GHz and f max = 1.06 THz at a moderate value of V DS = 0.75 V. In addition, we have physically modeled the abnormal peaky behavior in Mason's unilateral gain (U g ) at high values of VDS. A revised small signal model that includes a shunting R gd-NDR with negative value successfully describes the behavior of the device from 1 to 67 GHz.