Optical anisotropy in self-assembled InP quantum dots

Strong optical anisotropy is observed in the photoluminescence (PL) bands of both the InP self-assembled quantum dots and the ${\mathrm{Ga}}_{0.5}{\mathrm{In}}_{0.5}\mathrm{P}$ matrix. From the linearly polarized PL spectra measured under weak excitation, we found that large size quantum dots show strong anisotropy. The luminescence from a single quantum dot observed by the micro-PL technique revealed a doublet fine structure of the exciton levels that obey the linear polarization selection rule. The observed fine structure is shown to arise from an interplay of the electron-hole exchange interaction and the asymmetric crystal structure of the ${\mathrm{I}\mathrm{n}\mathrm{P}/\mathrm{G}\mathrm{a}}_{0.5}{\mathrm{In}}_{0.5}\mathrm{P}$ system.