Dimensionality of excitons in laser-diode structures composed ofInxGa1−xNmultiple quantum wells

Temperature dependence of radiative and nonradiative lifetimes of localized excitons has been assessed in the laser diode structures composed of ${\mathrm{In}}_{0.20}{\mathrm{Ga}}_{0.80}\mathrm{N}$ (3 nm)/${\mathrm{In}}_{0.05}{\mathrm{Ga}}_{0.95}\mathrm{N}$ (6 nm) multiple quantum well (MQW) [sample (a)] and ${\mathrm{In}}_{0.10}{\mathrm{Ga}}_{0.90}\mathrm{N}$ (3 nm)/${\mathrm{In}}_{0.02}{\mathrm{Ga}}_{0.98}\mathrm{N}$ (6 nm) MQW [sample (b)] by means of time-resolved photoluminescence spectroscopy. The radiative lifetimes $\left({\tau }_{\mathrm{rad}}\right)$ in sample (a) were almost constant around 6 ns between 23 K and 200 K, suggesting the mesoscopic effect where excitons are confined in the zero-dimensional potential such as a quantum-dot-like region. This interpretation fairly agrees with the result that the emission was ascribed to the localized excitons whose depth is about 250 meV. The ${\tau }_{\mathrm{rad}}$ value in sample (b) was 460 ps at 20 K and grew with increasing temperature. It was found that the depth of exciton localization in sample (b) is so weak that excitons reveal a nearly two-dimensional feature at RT as a result of the delocalization effect.