Effects of Strain and Spin–Orbit Coupling on the Electronic and Optical Properties of MoS₂ and MoSe₂ Monolayers

EFFECTS OF STRAIN AND SPIN–ORBIT COUPLING ON THE ELECTRONIC AND OPTICAL PROPERTIES OF MOS₂ AND MOSE₂ MONOLAYERS  

Dao Minh Duc¹, Assoc.Prof., Dr. Le Tien Ha¹, Assoc.Prof., Dr. Tran Quang Huy², Dr. Luong Thi Theu³

¹Thai Nguyen University of Sciences, Thai Nguyen University

²Faculty of Physics, Hanoi Pedagogical University 2

³Faculty of Economics and Fundamental Sciences, Hoa Binh University

Corresponding author: lttheu@daihochoabinh.edu.vn

Ngày nhận: 01/04/2026

Ngày nhận bản sửa: 03/4/2026

Ngày duyệt đăng: 24/4/2026

DOI: 10.71192/670136iwqkls

Abstract

This study systematically investigates the electronic and optical properties of monolayer MoX₂ (X = S, Se) under the combined effects of uniaxial strain and spin–orbit coupling (SOC) using density functional theory (DFT). The calculated band structures reveal that both MoS₂ and MoSe₂ exhibit direct band gaps at the K point, with values of approximately 1.78 eV and 1.44 eV, respectively. A significant SOC-induced splitting of the valence band maximum is observed, leading to the formation of two distinct excitonic transitions, namely A and B excitons. The energy separation between these excitons is found to be 0.15 eV for MoS₂ and 0.22 eV for MoSe₂. The influence of uniaxial strain is analyzed in the range of -5% to +5%, revealing that tensile strain reduces the band gap, whereas compressive strain slightly increases it. Notably, MoSe₂ exhibits a stronger sensitivity to strain compared to MoS₂. In addition, strain modifies the relative positions of band extrema and may induce a direct-to-indirect band gap transition under compressive conditions. Optical absorption spectra indicate strong excitonic peaks in the visible region, with clear strain-dependent shifts. MoS₂ exhibits higher exciton binding energy and sharper optical features, whereas MoSe₂ shows enhanced SOC effects and larger excitonic splitting. These findings highlight the critical interplay between strain and SOC in tuning the optoelectronic properties of two-dimensional transition metal dichalcogenides, providing valuable insights for the design of next-generation nanoscale optoelectronic and spintronic devices.

Key words: MoS₂ and MoSe₂ monolayers; Transition-metal dichalcogenides; Density functional theory; SOC; Excitons; Band structure; Density of states.

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