Spontaneous and piezoelectric polarization effects on electronic and optical properties of $\mathrm{ZnO}∕\mathrm{MgZnO}$ 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 $-0.070\mathrm{C}∕{\mathrm{m}}^2$ , which is larger than the value $(-0.050\mathrm{C}∕{\mathrm{m}}^2)$ for ZnO. The negligible internal field effect observed in the case of $\mathrm{ZnO}∕\mathrm{MgZnO}$ QW structures with relatively low Mg composition $(x<0.2)$ and thin well width $(L_w<46\mathrm{\AA })$ can be explained by the cancelation of the sum of piezoelectric and spontaneous polarizations between the well and the barrier. The $\mathrm{ZnO}∕\mathrm{MgZnO}$ QW laser has much larger optical gain than the $\mathrm{GaN}∕\mathrm{AlGaN}$ QW laser. This is attributed to the fact that the $\mathrm{ZnO}∕\mathrm{MgZnO}$ QW structure has a larger optical matrix element due to the relatively small internal field, compared to the $\mathrm{GaN}∕\mathrm{AlGaN}$ QW structure.

Optical properties of staggered 530 nm InGaN/InGaN/GaN quantum-well (QW) light-emitting-diodes are investigated using the multiband effective mass theory. These results are compared with those of conventional 530 nm InGaN/GaN QW structures. A staggered InGaN/InGaN/GaN QW structure is shown to have much larger spontaneous emission than a conventional InGaN/GaN QW structure. This can be explained by the fact that a staggered QW structure has much larger matrix element than a conventional QW structure because a spatial separation between electron and hole wave functions is substantially reduced with the inclusion of a staggered InGaN layer. A staggered QW structure shows that the peak position at a high carrier density (530 nm) is similar to that at a noninjection level.

Optical gain characteristics of $\mathrm{In}\mathrm{Ga}\mathrm{N}∕\mathrm{Ga}\mathrm{N}$ double quantum well (QW) structures with embedded AlGaN $\delta$ layer are investigated using the multiband effective mass theory. These results are compared with those of single QW structure without a $\delta$ layer. The theoretical energies show very good agreement with the experimental results for both single and double QW structures. The inclusion effect of a $\delta$ layer is found to be dominant at a relatively low carrier density. A double QW structure has larger optical gain than the single QW structure, in particular, at higher carrier density.

Optical properties of dip-shaped InGaN/GaN quantum well (QW) light-emitting diodes are investigated using the multiband effective-mass theory. These results are compared with those of conventional and staggered InGaN/GaN QW light-emitting diodes. In the case of a dip-shaped QW structure, the carrier density dependence of the transition wavelength is reduced due to a relatively small internal field effect. Also, we observe that the heavy-hole effective mass around the topmost valence band is greatly reduced with the inclusion of the dip-shaped layer. The spontaneous emission peak of a dip-shaped QW structure is shown to be larger than that of a staggered QW structure or a conventional QW structure. This is mainly due to the fact that a dip-shaped QW structure has larger optical matrix elements produced by Kane’s parameter.

Optical properties of blue AlInGaN/InGaN quantum well (QW) structures with a quaternary AlInGaN well layer were investigated by using the non-Markovian gain model with many-body effects. The band-gap expression of the AlInGaN materials was determined through a comparison with experimental results. We found that the emission peak can be enhanced by using quaternary AlInGaN well and is sensitive on In composition in the InGaN barrier. For example, the spontaneous emission coefficient for Al_0.08In_0.22Ga_0.67N/InxGa_1−xN QW structures shows a maximum at In composition of 0.13 in the barrier and gradually decreases with increasing In composition. This is attributed to the fact that the quasi-Fermi-level separation linearly decreases with increasing In composition in the barrier due to the decrease in the conduction and valence band offsets. The AlInGaN/InGaN system with zero internal field is found to have smaller emission peak than the AlInGaN/InGaN system with nonzero internal field due to smaller band offsets.