Single QD Spectroscopy

The surface QDs are visible as small brighter dots on the micrograph, showing that in such a mesa there are still many QDs. Samples with openings in a metaUic mask were prepared in the following way polystyrene nanobeads with diameters of 300 nm were dispersed on the sample, on which 100-nm aluminum were then deposited. The removal of the beads thus leaves circular openings in the aluminum mask [47]. 

The PL spectra of the smallest mesas display sharp fines that are typical of single QD fines. Single fines are better isolated on the high-energy side of the 

QD distribution owing to the lower spectral density of QD emission. However, no sharp lines could be isolated on the low energy side of the QD emission spectrum, for reasons that are so far not clear. We first checked that the intensity of these lines varies linearly with exciting power, in the low power regime this shows that the observed sharp lines correspond to the recombination of a single electron-hole pair and not to excited states recombination. 

The modeling of the particular experimental situation described in this work is done in detail in reference [55] and we shall present the main ideas and conclusions here. 

The coupling of localized electronic states to phonons was first described by Huang and Rhys [56] in their framework, the acoustic phonon modes are discretized and each individual mode forms a new eigenstate (an acoustic polaron) with each confined exciton state. Radiative transitions then occur between these polaron states, possibly leading to photon emission with emission or absorption of acoustic phonons. The probability of emission of an acoustic phonon depends on the coupling strength between the confined electron-hole pair state and the acoustic phonon mode, as well as on the phonon mode population (i.e. on the temperature). 

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