Towards low-loss telecom-wavelength photonic devices by designing GaBi$_{x}$As$_{1-x}$/GaAs core$-$shell nanowires

TL;DR

This study uses atomistic simulations to design GaBiAs/GaAs core-shell nanowires optimized for low-loss telecom-wavelength photonic devices, analyzing how composition and geometry affect optical properties and strain.

Contribution

It introduces a systematic analysis of composition, geometry, and strain effects in GaBiAs/GaAs nanowires for telecom applications, providing design guidelines for low-loss photonic devices.

Findings

Optimal nanowire configurations for 1.55 μm emission identified

Favorable properties found in nanowires with low diameter ratio (ρ_D ≤ 0.4)

Strain can be modulated from compressive to tensile by adjusting core thickness

Abstract

Nanowires are versatile nanostructures, which allow an exquisite control over bandgap energies and charge carrier dynamics making them highly attractive as building blocks for a broad range of photonic devices. For optimal solutions concerning device performance and cost, a crucial element is the selection of a suitable material system which could enable a large wavelength tunability, strong light interaction and simple integration with the mainstream silicon technologies. The emerging GaBiAs alloys offer such promising features and may lead to a new era of technologies. Here, we apply million-atom atomistic simulations to design GaBiAs/GaAs core-shell nanowires suitable for low-loss telecom-wavelength photonic devices. The effects of internal strain, Bi Composition (x), random alloy configuration, and core-to-shell diameter ratio ($\rm \rho_D$) are analysed and delineated by systematically varying these attributes and studying their impact on the absorption wavelength and charge carrier confinement. The complex interplay between x and $\rm \rho_D$ results in two distinct pathways to accomplish 1.55 um optical transitions: either fabricate nanowires with $\rm \rho_D \geq$ 0.8 and $x \sim$15\%, or increase $x$ to $\sim$30\% with $\rm \rho_D \leq$ 0.4. Upon further analysis of the electron hole wave functions, inhomogeneous broadening and optical transition strengths, the nanowires with $\rm \rho_D \leq$ 0.4 are unveiled to render favourable properties for the design of photonic devices. Another important outcome of our study is to demonstrate the possibility of modulating the strain character from a compressive to a tensile regime by simply engineering the thickness of the core region. The availability of such a straightforward knob for strain manipulation would be highly desirable for devices involving polarisation-sensitive light interactions.