Piezoelectric properties of Ga2O3: a first-principle study

The compounds exhibit piezoelectricity, which demands to break inversion symmetry, and then to be a semiconductor. For Ga2O3, the orthorhombic case (epsilon-Ga2O3) of common five phases breaks inversion symmetry. Here, the piezoelectric tensor of epsilon-Ga2O3 is reported by using density functional perturbation theory (DFPT). To confirm semiconducting property of epsilon-Ga2O3, its electronic structures are studied by using generalized gradient approximation (GGA) and Tran and Blaha's modified Becke and Johnson (mBJ) exchange potential. The gap value of 4.66 eV is predicted with mBJ method, along with the effective mass tensor for electron at the conduction band minimum (CBM) [about 0.24 m(0)]. The mBJ gap is very close to the available experimental value. The elastic tensor C-ij are calculated by using the finite difference method (FDM), and piezoelectric stress tensor e(ij) are attained by DFPT, and then piezoelectric strain tensor d(ij) are calculated from C-ij and e(ij). In this process, average mechanical properties of epsilon-Ga2O3 are estimated, such as bulk modulus, Shear modulus, Young's modulus and so on. The calculated d(ij) are comparable and even higher than commonly used piezoelectric materials such as alpha-quartz, ZnO, AlN and GaN.