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

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.