Temperature-dependent linewidth of single ${\mathrm{I}\mathrm{n}\mathrm{P}/\mathrm{G}\mathrm{a}}_x{\mathrm{In}}_{1-x}\mathrm{P}$ quantum dots: Interaction with surrounding charge configurations

We have investigated individual metal-organic vapor phase epitaxy-grown self-assembled InP quantum-dots in a ${\mathrm{Ga}}_{0.5}{\mathrm{In}}_{0.5}\mathrm{P}$ matrix by means of photoluminescence with high spatial resolution as a function of temperature and excitation density. We observe an abrupt change from the well-known but yet unclear relatively broad emission band at low temperatures to narrow lines at $T>~45\hspace{0.5em}\mathrm{K}.$ The high-temperature mode is the one expected for a fully confined quantum system. The ubiquitous broadening at low temperature is discussed in the framework of spectral diffusion, i.e., fluctuating charge configurations surrounding the quantum dot influence its transition energies. We conclude that the interacting charges are most probably trapped in connection with thickness variation in the wetting layer. Their release at higher temperatures removes the perturbation and leads to the expected appearance of sharp single dot spectra.