Design and properties of planar-type tunnel FETs using In0.53Ga0.47As/InxGa1-xAs/In0.53Ga0.47As quantum well

Abstract

Tunnel Field Effect Transistors (tunnel FETs) have been proposed using In0.53Ga0.47As/InxGa1-xAs/In0.53Ga0.47As Quantum Well (InxGa1-xAs QW) channels which improve their performance. It is expected in this structure that the high-In-content InxGa1-xAs QW layer with the lower bandgap can increase the tunneling current and resulting on-current (Ion), while the low-In-content In0.53Ga0.47As layer, where the source junction edge is mainly formed, can suppress the increase in the junction leakage current because of the higher bandgap. Considering the strain effect and the quantum confinement effect of the InxGa1-xAs QW layers, the In content and the QW thickness are designed carefully in terms of the reduction in the effective bandgap. The proposed tunnel FETs using the QW layers grown by Metal-organic Vapor Phase Epitaxy are fabricated, and the electrical and physical properties are systematically evaluated. It is found that the InxGa1-xAs QW can significantly enhance the performance of tunnel FETs. As expected in the calculation of the effective bandgap, the higher In content and thicker QW thickness lead to higher Ion, while the thinner QW thickness makes the sub-threshold swing (S.S.) steeper through the reduction in off-current (Ioff) and enhancement of carrier confinement. The minimum sub-threshold swing (S.S.min) of 62 mV/dec is obtained at VD = 150 mV for a tunnel FET with an In0.53Ga0.47As (2.6 nm)/In0.67Ga0.33 As (3.2 nm)/In0.53Ga0.47As (96.3 nm) QW structure. Also, the highest Ion of 11 μA/μm at VD = 150 mV and VG = 1 V, which is 8.5 times higher than 1.3 μA/μm of a control In0.53Ga0.47As tunnel FET, is obtained for a tunnel FET with an In0.53Ga0.47As (2.2 nm)/InAs (6.3 nm)/In0.53Ga0.47As (94.4 nm) QW structure. It is found that the InAs QW tunnel FETs with the InAs QW thicker than 5 nm significantly degrade by high junction leakage current attributed to the lattice relaxation.