The electronic structure of strained ZnO/MgxZn1-xOZnO/MgxZn1-xO superlattices and the influence of polarization

Based on the effective-mass model, the lower energies of the electron and the hole of ZnO/MgxZn1-xOZnO/MgxZn1-xO superlattices are calculated. Because of the mismatch of the lattice constant between the ZnO well and the MgxZn1-xOMgxZn1-xO barrier, piezoelectric and spontaneous polarization exist in ZnO/MgxZn1-xOZnO/MgxZn1-xO superlattices and a macroscopical internal electric field is found when well width Lw>4nm and Mg concentration x>0.2x>0.2. The parameters of ZnO/MgxZn1-xOZnO/MgxZn1-xO superlattices such as lattice constant, band offset, etc. are also proposed. Through calculations, we found the internal electric field can change the lowest energies of the electron and hole to 105.4 and 85.1 meV when well width LwLw up to 70 Å, which will influence the electronic and optical properties of ZnO/MgxZn1-xOZnO/MgxZn1-xO superlattices greatly, while the Rashba effect from the internal electric field is so small that it can be neglected. The ground state exciton energies with different Mg concentration xx are also calculated by variational method, our results are very close to the experimental results when Mg concentration x⩽0.3x⩽0.3.