Spontaneous and piezoelectric polarization effects in wurtzite ZnO/MgZnO quantum well lasers

Spontaneous and piezoelectric polarization effects on electronic and optical properties of ZnOMgZnO quantum well (QW) structures are investigated by using the non-Markovian gain model with many-body effects. The spontaneous polarization constant for MgO determined from a comparison with the experiment is about -0.070 C m2, which is larger than the value (-0.050 C m2) for ZnO. The negligible internal field effect observed in the case of ZnOMgZnO QW structures with relatively low Mg composition (x<0.2) and thin well width (Lw <46 Å) can be explained by the cancelation of the sum of piezoelectric and spontaneous polarizations between the well and the barrier. The ZnOMgZnO QW laser has much larger optical gain than the GaNAlGaN QW laser. This is attributed to the fact that the ZnOMgZnO QW structure has a larger optical matrix element due to the relatively small internal field, compared to the GaNAlGaN QW structure.