50-nm E-mode In0.7Ga0.3As PHEMTs on 100-mm InP substrate with fmax > 1 THz

We have demonstrated 50-nm enhancement-mode (E-mode) In_0.7Ga_0.3As PHEMTs with f_max in excess of 1 THz. The devices feature a Pt gate sinking process to effectively thin down the In_0.52Al_0.48As 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.