Quaternary 2D Monolayer Cu2Cl2Se2Hg2: Anisotropic Carrier Mobility and Tunable Bandgap for Transistor and Photocatalytic Applications.

Despite the advantages of quaternary 2D materials, fewer studies have been done on them than binary 2D materials. Calculations of quaternary 2D monolayer Cu2Cl2Se2Hg2 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 (PBE/HSE06) and demonstrates anisotropic carrier mobility. The electron mobility in the a direction is 1.2×103 cm2/V/s, which is significantly higher than the hole mobility of 0.48×103 cm2/V/s. In the b direction, the electron mobility is 1.01×103 cm2/V/s and is 8.9 times larger than the hole mobility of 0.11×103 cm2/V/s. The light absorption coefficients of Cu2Cl2Se2Hg2 are 1.0 ×105 /cm and 2.5 ×105 /cm 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 Cu2Cl2Se2Hg2, it is possible to increase the current ON/OFF ratio for field-effect transistors and to facilitate photocatalytic water splitting through a redox reaction. The research reveals that Cu2Cl2Se2Hg2, a 2D monolayer in the quaternary form, has promising capabilities as an alternative for creating crystal-oriented field-effect transistors and photocatalytic water splitting systems.