Quaternary 2D monolayer Cu₂Cl₂Se₂Hg₂: anisotropic carrier mobility and tunable bandgap for transistor and photocatalytic applications

Abstract Despite the advantages of quaternary two-dimensional (2D) materials, fewer studies have been done on them than binary 2D materials. Calculations of quaternary 2D monolayer Cu 2 Cl 2 Se 2 Hg 2 based on density functional theory and Green’s function surface analysis provide insights into its structural, dynamic, and thermal stability. This material has a direct band gap of 0.91/2.0 eV (Perdew–Burke–Ernzerhof/Heyd–Scuseria–Ernzerhof) and demonstrates anisotropic carrier mobility. The electron mobility in the a direction is 1.2 × 10 3 cm 2 V −1 s −1 , which is significantly higher than the hole mobility of 0.48 × 10 3 cm 2 V −1 s −1 . In the b direction, the electron mobility is 1.01 × 10 3 cm 2 V −1 s −1 and is 8.9 times larger than the hole mobility of 0.11 × 10 3 cm 2 V −1 s −1 . The light absorption coefficients of Cu 2 Cl 2 Se 2 Hg 2 are 1.0 × 10 5 cm −1 and 2.5 × 10 5 cm −1 in the visible and ultraviolet ranges, respectively. Uniaxial strain leads to an anisotropic alteration in the band gap and band edge position. By manipulating the strain direction and level in Cu 2 Cl 2 Se 2 Hg 2 , it is possible to increase the current ON/OFF ratio for field-effect transistors (FETs) and to facilitate photocatalytic water splitting through a redox reaction. The research reveals that Cu 2 Cl 2 Se 2 Hg 2 , a 2D monolayer in the quaternary form, has promising capabilities as an alternative for creating crystal-oriented FETs and photocatalytic water splitting systems.