Highly Modulated Dual Semimetal and Semiconducting Gamma-GeSe with Strain Engineering

TL;DR

This study reveals that Gamma-GeSe exhibits a thickness-dependent transition from semimetal to semiconductor, with strain engineering enabling tunable electronic properties, making it promising for nanoelectronics and solar cells.

Contribution

First-principles calculations demonstrate the unique thickness-dependent electronic transition and strain-tunable properties of Gamma-GeSe, a newly synthesized 2D material with high flexibility and anisotropic effective mass.

Findings

Gamma-GeSe transitions from semimetal to semiconductor with decreasing thickness.

1L Gamma-GeSe exhibits high flexibility and isotropic elastic properties.

Strain engineering induces indirect-direct and semiconductor-metal transitions.

Abstract

Layered hexagonal Gamma--GeSe, a new polymorph of GeSe synthesized recently, shows strikingly high electronic conductivity in its bulk form (even higher than graphite) while semiconducting in the case of monolayer (1L). In this work, by using first-principles calculations, we demonstrate that, different from its orthorhombic phases of GeSe, the Gamma--GeSe shows a small spatial anisotropic dependence and a strikingly thickness-dependent behavior with transition from semimetal (bulk, 0.04 eV) to semiconductor (1L, 0.99 eV), and this dual conducting characteristic realized simply with thickness control in Gamma-GeSe has not been found in other 2D materials before. The lacking of d-orbital allows charge carrier with small effective mass (0.16 m0 for electron and 0.23 m0 for hole) which is comparable to phosphorene. Meanwhile, 1L Gamma--GeSe shows a superior flexibility with Young's modulus of 86.59 N/m, only one-quarter of that of graphene and three-quarters of that of MoS2, and Poisson's ratio of 0.26, suggesting a highly flexible lattice. Interestingly, 1L Gamma-GeSe shows an in-plane isotropic elastic modulus inherent with hexagonal symmetry while an anisotropic in-plane effective mass owing to shifted valleys around the band edges. We demonstrate the feasibility of strain engineering in inducing indirect-direct and semiconductor-metal transitions resulting from competing bands at the band edges. Our work shows that the free 1L Gamma-GeSe shows a strong light absorption (~106 cm-1) and an indirect bandgap with rich valleys at band edges, enabling high carrier concentration and a low rate of direct electron-hole recombination which would be promising for nanoelectronics and solar cell applications.