Enhancement-mode GaN-based junctionless vertical surrounding-gate transistor with dual-material gate structure for high-frequency applications

In this paper, we propose an enhancement-mode (E-mode) GaN-based junctionless field-effect transistor (FET) with a dual-material gate (DMG) structure for high-frequency performance. Its device performance is analyzed and compared with a single-material gate (SMG) device using device simulator. The DMG structure improves the drain current (I_DS) and transconductance (g_m) because of an increase in the electron velocity in the channel region. The gate capacitance (C_gg) of the DMG structure is also decreased by reducing the gate-to-channel capacitance (C_gc) component in the gate-to-source capacitance (C_gs). Thus, the RF performance of DMG devices improves owing to the increase in g_m and the decrease in C_gg. In addition, we examine the effect of structural variables on the performance of the DMG device. The current performance of the DMG device changes depending on the influence on the current flow in the channel region. The DMG device with an Ni-gate length (L_Ni-gate) of 30 nm and a smaller nanowire radius (R) enhances the maximum g_m (g_{m, max}) by increasing the effect of the DMG structure. The threshold voltage (V_th) can also be affected by L_Ni-gate and R. A positive V_th can be obtained by forming a channel region fully depleted by a longer L_Ni-gate and a smaller R. Consequently, the excellent E-mode high-frequency devices can be realized by structural optimization.