Resonant photoluminescence and excitation spectroscopy of CdSe/ZnSe and CdTe/ZnTe self-assembled quantum dots

TL;DR

This study investigates the excitation mechanisms in II-VI self-assembled quantum dots, identifying direct excited state transitions and phonon-assisted processes, with implications for understanding their optical properties.

Contribution

It provides a detailed analysis of excitation mechanisms in CdSe/ZnSe and CdTe/ZnTe quantum dots, distinguishing between electronic transitions and phonon interactions.

Findings

Direct excited state - ground state transitions produce sharp spectral lines.

Phonon-assisted absorption dominates in smaller quantum dots.

Resonant photoluminescence spectra reveal separate contributions of excitation mechanisms.

Abstract

We show that two major carrier excitation mechanisms are present in II-VI self-assembled quantum dots. The first one is related to direct excited state - ground state transition. It manifests itself by the presence of sharp and intense lines in the excitation spectrum measured from single quantum dots. Apart from these lines, we also observe up to four much broader excitation lines. The energy spacing between these lines indicates that they are associated with absorption related to longitudinal optical phonons. By analyzing resonantly excited photoluminescence spectra, we are able to separate the contributions from these two mechanisms. In the case of CdTe dots, the excited state - ground state relaxation is important for all dots in ensemble, while phonon - assisted processes are dominant for the dots with smaller lateral size.