Multichannel Depletion-Type Field-Effect Transistor Based on Ferromagnetic Germanene

Jun Zheng,Yong Guo,Chunlei Li,Feng Chi,Ruiyang Yuan,Yang Xiang

doi:10.1103/physrevapplied.16.024046

Abstract

Based on ferromagnetic germanene, we theoretically propose a multichannel depletion-type field-effect transistor (FET) operated by a vertical electric field. The electron transport properties of the topological transistor are investigated through the nonequilibrium Green's function method. The results reveal that new edge channels can be formed by removing some $\mathrm{Ge}$ atoms along the $x$ axis of the device. The proposed multichannel ferromagnetic germanene transistor has a twice on-state current and half subthreshold swing than that of traditional germanene FETs. Under the coaction of electric induced staggered potential and staggered exchange field, both the $100\mathrm{%}$ spin-polarized edge states and valleys can be achieved. The ferromagnetic germanene FET can be turned off just by adjusting the electric field. In the low electric field conditions, the switching-off mechanism is due to spin blocking caused by the edge-state mismatch, while for relatively high electric field cases, both the edge-state mismatch and energy-valley mismatch are utilized. With the moderate increase in the exchange field, the switching mechanism is not changed, but the threshold electric field and breakdown voltage of the FET can be, respectively, reduced and enhanced significantly. All the results indicate that the proposed ferromagnetic germanene FET is a promising candidate for ultra-low-power dissipation topological devices.

Highlights

Germanene is a type of two-dimensional (2D) topological insulator consisting of germanium (Ge) atoms arranged to graphene and silicene in a hexagonal structure
(1) When Ge atoms are removed along the x axis, two new edge channels with opposite spin are created at the boundary, the on state current of the multichannel germanene field-effect transistor (FET) at λE = 0 can be up to double
(2) When the staggered potential satisfies λE > λSO − M + VDS/2, the edge state transformed from the quantum spin Hall state to the spin-polarized quantum anomalous Hall state, and the K and K valleys are +100% or −100% spin polarized in different energy ranges

Summary

INTRODUCTION

Germanene is a type of two-dimensional (2D) topological insulator consisting of germanium (Ge) atoms arranged to graphene and silicene in a hexagonal structure. In 1994, a decade before the successful fabrication of graphene, the structure of germanene was studied by Takeda and Shiraishi using density functional theory [1]. In 2011, the theoretical study of Yao et al [9] confirmed that germanene tends to form a low-buckled structure rather than a planar one, and Ge atoms with a 2D honeycomb geometry have nontrivial topological properties in their native structure. A tunable direct band gap can be opened at the Dirac point [10,11,12,13,14] Based on these properties, a variety of silicene and germanene field-effect topological transistors have been proposed based on theory [15,16,17,18,19,20,21]. It should be pointed out that even though its structure is similar to that of a normal germanene FET, which requires only band gaps to turn the transistor off, the fundamental switching mechanism of the FM germanene FET is completely different

MODEL AND METHODS

RESULTS AND DISCUSSION

CONCLUSIONS