Observation of quantum dot-like behavior of GaInNAs in GaInNAs/GaAs quantum wells

We report a quantum dot-like behavior of GaInNAs due to composition nonuniformity of N and In in GaInNAs/GaAs quantum wells (QWs). Images of cross-sectional transmission electron microscopy show that the wells of both ${\mathrm{Ga}}_{\mathrm{0.7}}{\mathrm{In}}_{\mathrm{0.3}}\mathrm{As/GaAs}$ and ${\mathrm{Ga}}_{\mathrm{0.7}}{\mathrm{In}}_{\mathrm{0.3}}{\mathrm{N}}_{\mathrm{0.02}}{\mathrm{As}}_{\mathrm{0.98}}\mathrm{/GaAs}$ are undulated due to lateral variations in strain. This effect is more pronounced in the N-containing QWs due to nonuniform In and N concentrations. Rapid thermal annealing causes a blueshift of the photoluminescence (PL) peak, and results in a splitting of the as-grown broad PL emission into two peaks. The In and N composition fluctuation after annealing becomes predominantly bimodal. The low-energy $P_L$ peak is attributed to excitons localized at deep levels, which are originated from In- and N-rich regions in the wells acting as quantum dots (QD). The high-energy peak $P_H$ is likely due to the excitons of the 2D QWs. To reduce the local strain, N atoms are preferentially localized in the In-rich regions, so the separation between these two peaks increases with increasing N concentration. Increasing excitation intensity results in a significant blueshift for $P_L$ and little blueshift for $P_H,$ due to the easier band filling of the localized QD states than QW states.