Comparison of Zn_{1-x}Mn_xTe/ZnTe multiple-quantum wells and quantum dots by below-bandgap photomodulated reflectivity

TL;DR

This study compares the optical properties and strain states of Zn_{1-x}Mn_xTe/ZnTe quantum dots and their parent heterostructures, revealing fabrication-induced strain changes without additional confinement effects.

Contribution

It provides a detailed analysis of how nanofabrication alters strain in quantum dots compared to heterostructures, using photomodulated reflectivity and theoretical calculations.

Findings

Quantum dots are freestanding with altered strain states.

No additional confinement effects observed due to lateral size.

Main fabrication effect is a change in strain state.

Abstract

Large-area high density patterns of quantum dots with a diameter of 200 nm have been prepared from a series of four Zn_{0.93}Mn_{0.07}Te/ZnTe multiple quantum well structures of different well width (4 nm, 6 nm, 8 nm and 10 nm) by electron beam lithography followed by Ar+ ion beam etching. Below-bandgap photomodulated reflectivity spectra of the quantum dot samples and the parent heterostructures were then recorded at 10 K and the spectra were fitted to extract the linewidths and the energy positions of the excitonic transitions in each sample. The fitted results are compared to calculations of the transition energies in which the different strain states in the samples are taken into account. We show that the main effect of the nanofabrication process is a change in the strain state of the quantum dot samples compared to the parent heterostructures. The quantum dot pillars turn out to be freestanding, whereas the heterostructures are in a good approximation strained to the ZnTe lattice constant. The lateral size of the dots is such that extra confinement effects are not expected or observed.