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
0.7
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.