Electronic and optical properties of ZnO quantum dots under hydrostatic pressure

In the present work, we studied the electronic and optical properties of ZnO quantum dots (QDs) subjected to externally applied hydrostatic pressure. Our single-particle calculations are based on the empirical pseudopotential method and the excitonic effects are considered by employing the configuration interaction approach. The optical band gap, Stokes shift, and optical emission polarization have been investigated as a function of the applied pressure. It is found that the applied pressure causes a linear increase in the optical band gap. The pressure coefficient appears to be highly size dependent, exhibiting a monotonic increase with increasing QD size. In contrast to this monotonic behavior, the applied pressure induces a nonmonotonic Stokes shift which presents a minimum value at a critical pressure. For pressures larger than this critical value, the optical emission polarization exhibits a sharp transition from in-plane to out-of-plane polarization. Finally, it is found that the critical pressure at which the crossing takes place strongly depends on the QD size, showing larger values for larger QD sizes. Beyond this crossing point, the lowest optically bright exciton state mainly originates from one Slater determinant, where both the single-particle electron and hole states have an S-type envelope function and the hole state originates mainly from the bulk Bloch C band. DOI: 10.1103/PhysRevB.87.125302