Atomistic Modeling of Fine Structure Splitting in InGaN/GaN Dot-in-Nanowire Structures for Use in Entangled Photon Pair Generation

Fine structure splitting (FSS) is a bottleneck in quantum dot (QD) based solid-state entangled photon pair sources for application in quantum key distribution (QKD). In QDs, entangle photon pairs are generated through a cascaded emission process: biexciton to exciton to the ground state. The FSS of the excitonic states destroys the entanglement of the photon pairs; hence, it needs to be eliminated. For numerical investigation of FSS and design optimization, a multiscale-multiphysics many-body calculation is required. In this article, we report the coupling of a full configuration interaction (FCI) method with a 10-band (sp
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s*-spin) tight-binding (TB) model to calculate the excitonic energetics of realistically sized InGaN/GaN dot-innanowire structures. Model benchmarking has been done against a recently reported InGaN/GaN multiple quantum well (MQW) structure in the a -plane orientation. Computational methodology of implementing a hexagonal-base truncated pyramid shaped QD has been presented. The effects of QD shape/thickness, material composition, and crystal growth direction (polar c-plane and non-polar m -plane and α-plane) on the FSS of InGaN/GaN based photon emitters have been investigated. Polarization profiles of the emitted photons from the excitonic transitions have been derived quantum mechanically from transition dipole moments. With the smallest FSS, the non-polar m-plane device has been found to be most promising for the QKD application.