Highly modulated dual semimetal and semiconducting γ-GeSe with strain engineering

Abstract

Layered hexagonal γ-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 γ-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 γ-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 γ-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 γ-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 γ-GeSe shows a strong light absorption (~10^6 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.

First-Principles Study of the Phonon Lifetime and Low Lattice Thermal Conductivity of Monolayer γ-GeSe: A Comparative Study

“…The optimized lattice parameters are listed in Table 1, which are consistent with the experimentally and theoretically reported values. 19,22,39 The calculated phonon dispersion curves are shown in Figure 2, which fits well with the result reported, 19,22,23 and no imaginary frequencies exist, indicating that the monolayer structures of the three GeSe phases are dynamically stable. Due to the four atoms in the primitive cell, there are 12 phonon modes (three acoustic modes and nine optical modes) in monolayer GeSe.…”

Centimeter‐Scale PdS2 Ultrathin Films with High Mobility and Broadband Photoresponse

“…As for thermostability for PdS 2 and PdS, the energy and crystalline structure show a small fluctuation, confirming their excellent thermostability at 700 K, which is aligned with the experimental result. [ 29–31 ]…”

“…As for thermostability for PdS 2 and PdS, the energy and crystalline structure show a small fluctuation, confirming their excellent thermostability at 700 K, which is aligned with the experimental result. [29][30][31] After confirming the relationship between temperature and PdS 2 , we focus on its physical properties research. Angleresolved polarized Raman spectroscopy is used to verify the inherent in-plane anisotropy of PdS 2 films.…”

Abnormal behavior of preferred formation of the cationic vacancies from the interior in a γ-GeSe monolayer with the stereo-chemical antibonding lone-pair state

“…10 Unlike theoretical predictions, the deposited γ-GeSe shows an A–B′ stacked non-centrosymmetric atomic structure. 11 This new structure has aroused great interest with respect to the strain-tunable electronic structure and spontaneous polarization, 12,13 van der Waals heterostructures, 14 and fast Li-ion intercalation properties 15 through first-principles calculations.…”