Effects of HfO₂/Al₂O₃ gate stacks on electrical performance of planar In<i> _x </i>Ga₁₋ <i> _x </i>As tunneling field-effect transistors

Abstract

We study the impact of gate stacks on the electrical characteristics of Zn-diffused source InxGa1−xAs tunneling field-effect transistors (TFETs) with Al2O3 or HfO2/Al2O3 gate insulators. Ta and W gate electrodes are compared in terms of the interface trap density (Dit) of InGaAs MOS interfaces. It is found that Dit is lower at the W/HfO2/Al2O3 InGaAs MOS interface than at the Ta/HfO2/Al2O3 interface. The In0.53Ga0.47As TFET with a W/HfO2 (2.7 nm)/Al2O3 (0.3 nm) gate stack of 1.4-nm-thick capacitance equivalent thickness (CET) has a steep minimum subthreshold swing (SS) of 57 mV/dec, which is attributed to the thin CET and low Dit. Also, the In0.53Ga0.47As (2.6 nm)/In0.67Ga0.33As (3.2 nm)/In0.53Ga0.47As (96.5 nm) quantum-well (QW) TFET supplemented with this 1.4-nm-thick CET gate stack exhibits a steeper minimum SS of 54 mV/dec and a higher on-current (Ion) than those of the In0.53Ga0.47As TFET.