Ultra-low thermal conductivity and high thermoelectric performance of two-dimensional Ga2O2: A comprehensive first-principles study

Gallium oxide such as two-dimensional (2D) Ga2O3 monolayers has been widely used in lasers, dielectric coatings for solar cells, low-dimensional electronic and optoelectronic device applications due to their excellent electrical optical and thermal properties. In this work, we predicted a new 2D gallium oxide Ga2O2 and systematically investigated its stability, electronic properties, and thermoelectric performance. The phonon dispersion, elastic tensor and ab initio molecular dynamics simulations show that the Ga2O2 monolayer is dynamically, mechanics and thermally stable. We find the Ga2O2 monolayer is an indirect semiconductor with a wide band gap of 2.77 eV and high electron mobility. In particular, 2D Ga2O2 has extremely low thermal conductivity and the optical phonons dominate the thermal conductivity. By analyzing its harmonic and anharmonic properties, we find that the weak interaction between Ga atoms is the main reason for this phenomenon. At last, we predict that the maximum ZT values of 2D Ga2O2 are evaluated up to 6.5 at 500 K and 3.3 at 300 K, respectively. With ultra-low thermal conductivity and high thermoelectric performance, 2D Ga2O2 is considered a potential candidate for thermoelectric materials.