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

Changmeng Huan; Yongqing Cai; Devesh R Kripalani; Kun Zhou; Qingqing Ke

doi:10.1039/d2nh00573e

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

Nanoscale Horiz. 2023 Feb 27;8(3):404-411. doi: 10.1039/d2nh00573e.

Authors

Changmeng Huan^{1

2}, Yongqing Cai³, Devesh R Kripalani⁴, Kun Zhou⁴, Qingqing Ke^{1

2}

Affiliations

¹ School of Microelectronics Science and Technology, Sun Yat-sen university, Zhuhai 519082, China. keqingq@mail.sysu.edu.cn.
² Guangdong Provincial Key Laboratory of Optoelectronic Information Processing Chips and Systems, Sun Yat-sen University, Zhuhai 519082, China.
³ Joint Key Laboratory of the Ministry of Education, Institute of Applied Physics and Materials Engineering, University of Macau, Taipa, Macau, China. yongqingcai@um.edu.mo.
⁴ School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore.

PMID: 36723237
DOI: 10.1039/d2nh00573e

Abstract

Two-dimensional (2D) materials tend to have the preferable formation of vacancies at the outer surface. Here, contrary to the normal notion, we reveal a type of vacancy that thermodynamically initiates from the interior part of the 2D backbone of germanium selenide (γ-GeSe). Interestingly, the Ge-vacancy (V_Ge) in the interior part of γ-GeSe possesses the lowest formation energy amongst the various types of defects considered. We also find a low diffusion barrier (1.04 eV) of V_Ge, which is half of those of sulfur vacancies in MoS₂. The facile formation of mobile V_Ge is rooted in the antibonding coupling of the lone-pair Ge 4s and Se 4p states near the valence band maximum, which also exists in other gamma-phase MX (M = Sn, Ge; X = S, Te). The V_Ge is accompanied by a shallow acceptor level in the band gap and induces strong infrared light absorption and p-type conductivity. The V_Ge located in the middle cationic Ge sublattice is well protected by the surface Se layers - a feature that is absent in other atomically thin materials. Our work suggests that the unique well-buried inner V_Ge, with the potential of forming structurally protected ultrathin conducting filaments, may render the GeSe layer an ideal platform for quantum emitting, memristive, and neuromorphic applications.