Excitonic fine structure of epitaxial Cd(Se,Te) on ZnTe type-II quantum dots

TL;DR

This study combines experimental photoluminescence spectroscopy and theoretical calculations to analyze how the excitonic fine structure in Cd(Se,Te) quantum dots embedded in ZnTe changes with Se content, revealing a transition from type-I to type-II behavior and novel confinement properties.

Contribution

It provides a comprehensive experimental and theoretical analysis of excitonic fine structure evolution in Cd(Se,Te) quantum dots, highlighting the transition from type-I to type-II and discovering unique confinement regimes.

Findings

Fine-structure splitting decreases with increased Se content.

Transition from type-I to type-II transition occurs as Se increases.

Existence of a mixed confinement regime with unique excitonic properties.

Abstract

The structure of the ground state exciton of Cd(Se,Te) quantum dots embedded in ZnTe matrix is studied experimentally using photoluminescence spectroscopy and theoretically using ${\bf k}\cdot{\bf p}$ and configuration interaction methods. The experiments reveal a considerable reduction of fine-structure splitting energy of the exciton with increase of Se content in the dots. That effect is interpreted by theoretical calculations to originate due to the transition from spatially direct (type-I) to indirect (type-II) transition between electrons and holes in the dot induced by increase of Se. The trends predicted by the theory match those of the experimental results very well.The theory identifies that the main mechanism causing elevated fine-structure energy in particular in type-I dots is due to the multipole expansion of the exchange interaction. Moreover, the theory reveals that for Se contents in the dot $>0.3$, there exist also a {\bf peculiar type of confinement showing signatures of both type~I and type~II} and which exhibits extraordinary properties, such as almost purely light hole character of exciton and toroidal shape of hole states.