We describe carrier–carrier interaction in self-assembled In0.5Ga0.5As quantum dots (QDs) at room temperature. The spectral shift and linewidth broadening of ground state emission as a function of the excitation density are investigated through near-field single quantum dot photoluminescence spectroscopy. From the viewpoint of excitation density dependent spectral broadening of the ground state emission, we discuss the dephasing process in QDs due to Coulomb interaction.

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The observation of photoluminescence spectra of self-assembled single InGaAs quantum dots at room temperature was performed under weak excitation conditions using a near-field scanning optical microscope. Operation in illumination-collection mode with a highly sensitive double-tapered optical fibre probe enabled detection of weak photoluminescence signals at room temperature with high efficiency and high spatial resolution. Each single quantum dot was imaged with a spatial resolution of about 250 nm, which corresponded to a quarter of the wavelength of the photoluminescence from quantum dots. The photoluminescence yields of individual quantum dots were widely distributed and were found to decrease with photoluminescence energy. This result serves as a clue to be pursued for better understanding of the thermal excitation of the carrier from confined states in quantum dots.

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