Theoretical analysis of influence of random alloy fluctuations on the opto-electronic properties of site-controlled (111)-oriented InGaAs/GaAs quantum dots

TL;DR

This study uses a tight-binding model to analyze how random alloy fluctuations affect the electronic and optical properties of (111)-oriented InGaAs/GaAs quantum dots, highlighting their potential for entangled photon sources.

Contribution

It provides a detailed theoretical analysis of alloy fluctuation effects on quantum dot properties, emphasizing size-dependent reduction of these effects and implications for quantum photonics.

Findings

Alloy fluctuations impact diminishes with increasing dot size.

Optical anisotropy in the (111) plane is nearly eliminated.

Reduced fine structure splitting suggests suitability for entangled photon generation.

Abstract

We use an $sp^3d^5s^* $ tight-binding model to investigate the electronic and optical properties of realistic site-controlled (111)-oriented InGaAs/GaAs quantum dots. Special attention is paid to the impact of random alloy fluctuations on key factors that determine the fine-structure splitting in these systems. Using a pure InAs/GaAs quantum dot as a reference system, we show that the combination of spin-orbit coupling and biaxial strain effects can lead to sizeable spin-splitting effects in these systems. Then, a realistic alloyed InGaAs/GaAs quantum dot with 25\% InAs content is studied. Our analysis reveals that the impact of random alloy fluctuations on the electronic and optical properties of (111)-oriented InGaAs/GaAs quantum dots reduces strongly as the lateral size of the dot increases and approaches realistic sizes. For instance the optical matrix element shows an almost vanishing anisotropy in the (111)-growth plane. Furthermore, conduction and valence band mixing effects in the system under consideration are strongly reduced compared to standard (100)-oriented InGaAs/GaAs systems. All these factors strongly indicate a reduced fine structure splitting in site-controlled (111)-oriented InGaAs/GaAs quantum dots. Thus, we conclude that quantum dots with realistic (50-80~nm) base length represent promising candidates for polarization entangled photon generation, consistent with recent experimental data.