First-principles method based electronic transport properties of two-dimensional SnSe_(2(1-x))X_(2x) alloys

摘要

SnSe_2 based layered 2-dimensional alloys have drawn much attention due to their excellent optical and electronic properties in which substitutional doping is a well-defined route to modulate functionalities of devices made up of these novel materials. Herein, by using the first-principles method based density functional theory in conjunction with Boltzmann transport equation, we systematically investigate the stability, electronic structure and transport properties of the monolayer of SnSe_(2(1-x))O_(2x) and SnSe_(2(1-x))S_(2x) alloys at 300 K. Our results reveal that oxygen and sulphur behave as iso-electronic dopants and they do not alter the intrinsic nature of the pristine monolayer SnSe_2. The calculated indirect band gap of monolayer pristine SnSe_2, SnSe_(2(1-x))O_(2x), and SnSe_(2(1-x))S_(2x) is 0.79 eV, 0.78 eV, and 0.77 eV, respectively, at the compositional proportion x (0 ≤ x ≤ 0.125). These dopants create energy states near the band edge of the monolayer SnSe_2. Moreover, the corresponding effective masses have been calculated at the curvature of the band edge using the least square fitting. Electrical conductivity (σ/τ), Seebeck coefficient (S) and thermoelectric power factor (PF/τ) are calculated as a function of chemical potential. At the studied chemical potential range, for the pristine monolayer SnSe_2 the achieved maximum electrical conductivity, Seebeck coefficient, and thermoelectric power factor are 6.0×10~(19) Ω~(-1)m~(-1)s~(-1), 1.25 mV/K and 1.28×10~(11) Wm~(-1)K~(-2)s~(-1) respectively. Moreover, for SnSe_(2(1-x))S_(2x) and SnSe_(2(1-x))S_(2x), the achieved electrical conductivity, Seebeck coefficient, and thermoelectric power factor are 4.5×10~(19) and 5.8×10~(19) Ω~(-1)m~(-1)s~(-1), 1.15 and 1.32 mV/K, and 7.2×10~(10) and 1.23×10~(11) Wm~(-1)K~(-2)s~(-1), respectively. This contribution provides an effective way to understand and improve the transport properties of 2D ternary semiconductor SnSe_(2(1-x))X_(2x) alloys based devices which have potential applications in next-generation integrated optoelectronics due to their flexible and tunable band gap.