Light-hole states in a strained quantum dot: numerical calculation and phenomenological models

TL;DR

This paper combines numerical and phenomenological models to analyze how built-in strain affects light-hole and heavy-hole states in strained quantum dots, revealing significant state mixing and property modifications relevant across various heterostructures.

Contribution

It introduces and tests phenomenological models for strain effects on hole states in quantum dots based on detailed numerical solutions, highlighting the role of light-hole state interactions.

Findings

Built-in axial strain determines the hole ground state character.

Strain induces significant mixing between light-hole and split-off states.

Modifications in spin, anisotropy, and oscillator strength are observed due to state mixing.

Abstract

Starting from the numerical solution of the 6-band \textbf{k.p} description of a lattice-mismatched ellipsoidal quantum dot situated inside a nanowire, including a spin Zeeman effect with values appropriate to a dilute magnetic semiconductor, we propose and test phenomenological models of the effect of the built-in strain on the heavy hole, light hole and exciton states. We test the validity and the limits of a description restricted to a ($\Gamma_8$) quadruplet of ground states and we demonstrate the role of the interactions of the light-hole state with light-hole excited states. We show that the built-in axial strain not only defines the character, heavy-hole or light-hole, of the ground state, but also mixes significantly the light-hole state with the split-off band's states: Even for a spin-orbit energy as large as 1 eV, that mixing induces first-order modifications of properties such as the spin value and anisotropy, the oscillator strength, and the electron-hole exchange, for which we extend the description to the light-hole exciton. CdTe/ZnTe quantum dots are mainly used as a test case but the concepts we discuss apply to many heterostructures, from mismatched II-VI and III-V quantum dots and nanowires, to III-V nanostructures submitted to an applied stress and to silicon nanodevices with even smaller residual strains.