Tuning the electronic and piezoelectric properties of Janus Ga2XY (X/Y=S, Se, Te) monolayers: A first-principles calculation

The quest for novel materials exhibiting significant piezoelectricity remains imminent. Herein, the piezoelectricity of Janus Ga2XY (X/YS, Se, Te) monolayers has been investigated by DFT calculation. The results show that in-plane piezoelectric coefficients d(11) of Ga2SSe, Ga2STe, Ga2SeTe are 3.08, 4.76, 3.55 p.m./V, and out-of-plane piezoelectric coefficients d(31) are 0.14, 0.45, 0.33 pm/V. In addition, the vertical mirror asymmetry and different charge distributions lead to large piezoelectric properties of Ga2STe. Notably, strain can effectively regulate the piezoelectric properties of Janus Ga2XY monolayers. Under tensile strain, the piezoelectric stress coefficients (e(11)) of Ga2XY increase and the elastic stiffness coefficients (C-11+C-12, C-11-C-12) decrease, resulting in significant piezoelectric coefficients (d(11) and d(31)), which can be attributed to an increase in Born effective charge Z(xx)* and a decrease in the bond force. The results establish a theoretical foundation for the application of novel 2D Janus Ga2XY monolayers in piezoelectric devices.