Fringing Effect of V-Gate on Heterojunction Doped-Channel Field-Effect Transistors

Fringing effect of V-gate heterojunction doped-channel field effect transistors (HDCFETs) were investigated in detail. V-gate with a 0.12-μm gate-metal footprint on HDCFET was successful fabricated through 1-μm photoresist opening using conventional optical lithography. The measurement dc and high-frequency characteristics; transconductance (g_D), output conductance (g_m), higher unity-current gain f_t) and unity-power gain frequencies(f_max) are 200 mS/mm, 3.5 mS/mm, 21 GHz and 32 GHz, respectively. Fringing effects of lateral and vertical removal of triangular region of GaAs sacrificial layer below the V-gate metal were simulated by semiconductor simulator-ATLAS. Simulated results reveal that both triangular-metal fringe and underneath material play an important role on HDCFET dc and ac performances. Experimental and simulated results conclude that; the triangular-metal fringe is of advantage to improve the modulation of channel and enhance dc performances but gate fringing capacitance due to the triangular-metal fringe and the 0.455-μm sacrificial layer increase the total gate-to-source capacitance (C_GS) to decrease ac performances, even if there is no sacrificial layer upon the Schottky layer, the triangular-metal fringe still contributes 15 % capacitance to the total gate-to-source capacitance