Substrate-induced asymmetric charge distribution tuning the thermal transport and electronic properties of two-dimensional GaX (X=S and Se)

GaS and GaSe, as members of the III-VI group compounds, have garnered significant attention due to their excellent optoelectronic properties. Recent studies have highlighted the low lattice thermal conductivity (TC) and excellent thermoelectric properties of two-dimensional (2D) GaX (X=S and Se). However, these investigations have focused on free-standing GaX, overlooking the substrate effect. In our study, we conducted first-principles calculations to assess the thermal transport and electronic properties of 2D free-standing and supported GaX (X=S, Se). In terms of thermal transport properties, our findings reveal a significant reduction in the lattice TC of 2D GaS and GaSe when supported on substrates. When supported on the h-BN (0001) substrate, the reductions are 68.01 % and 80.34 %, respectively. Similarly, when supported on the β-Si3N4 (0001) substrate, the lattice TC of 2D GaS and GaSe decreases by 74.60 % and 88.73 %, respectively. The significant decrease in lattice TC is primarily from the asymmetric bonding of GaX induced by the substrates, which enhances phonon anharmonicity and reduces phonon lifetime. In the realm of electronic properties, our investigations reveal that the influence exerted by the h-BN substrate upon the energy band structure of supported GaX is minimal, whereas β-Si3N4 substrate has a greater effect on the energy band structure of the supported GaX due to its high and low undulating atomic surface. Our findings underscore the remarkable tunability of both lattice TC and electronic properties in 2D GaX by selecting different substrates, which holds significant promise for the future applications of 2D GaX in emerging technologies.