Tunable Electronic and Topological Properties of Germanene by Functional Group Modification.

Shu-Feng Zhang,Ceng-Ceng Ren,Pei-Ji Wang,Wei-Xiao Ji,Chang-Wen Zhang,Ping Li

doi:10.3390/nano8030145

Abstract

Electronic and topological properties of two-dimensional germanene modified by functional group X (X = H, F, OH, CH3) at full coverage are studied with first-principles calculation. Without considering the effect of spin-orbit coupling (SOC), all functionalized configurations become semiconductors, removing the Dirac cone at K point in pristine germanene. We also find that their band gaps can be especially well tuned by an external strain. When the SOC is switched on, GeX (X = H, CH3) is a normal insulator and strain leads to a phase transition to a topological insulator (TI) phase. However, GeX (X = F, OH) becomes a TI with a large gap of 0.19 eV for X = F and 0.24 eV for X = OH, even without external strains. More interestingly, when all these functionalized monolayers form a bilayer structure, semiconductor-metal states are observed. All these results suggest a possible route of modulating the electronic properties of germanene and promote applications in nanoelectronics.

Highlights

Due to the novel electronic properties, graphene has attracted plenty of interest since its discovery [1,2,3,4,5], including massless Dirac fermion, high thermal conductivity, and high carrier mobility (200,000 cm2/(v s)) [6,7]
Without considering the effect of spin-orbit coupling (SOC), we find that chemical modification will remove the Dirac point at Fermi level and open a direct band gap at Γ point, and which may be well tuned by external strain
We mainly focus on the four-symmetrical functionalized germanene monolayers

Summary

Introduction

Due to the novel electronic properties, graphene has attracted plenty of interest since its discovery [1,2,3,4,5], including massless Dirac fermion, high thermal conductivity, and high carrier mobility (200,000 cm2/(v s)) [6,7]. Flexibility of graphene is essential for flexible nanoelectronics, which has produced a lot of products in experiments [8,9,10]. It has a thermal conductivity of 5000 Wm−1 K−1 at room temperature, offering an advantage for membrane technology [11]. The prediction and measurement of more 2D TI materials, especially those with large band gaps, is still challenging These difficulties promote the study of tuning the electronic properties of graphene [20,21]; geometric or chemical modifications are two widely used methods. It encourages great efforts regarding the search for other honeycomb films composed of heavier group–IV elements such as silicon (Si), germanene (Ge), stanene (Sn) and plumbene (Pb) [22,23,24,25,26,27,28], as well as other group-V films

Methods

Results

Conclusion