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