Impact of Disorder on the Optoelectronic Properties of GaNyAs1−x−yBix Al

Abstract

We perform a systematic theoretical analysis of the nature and importance of alloy disorder effects on the electronic and optical properties of GaNyAs1−x−yBix alloys and quantum wells (QWs), using large-scale atomistic supercell electronic structure calculations based on the tight-binding method. Using ordered alloy supercell calculations we also derive and parametrise an extended basis 14-band k·p Hamiltonian for GaNyAs1−x−yBix. Comparison of the results of these models highlights the role played by short-range alloy disorder -associated with substitutional nitrogen (N) and bismuth (Bi) incorporation -in determining the details of the electronic and optical properties. Systematic analysis of large alloy supercells reveals that the respective impact of N and Bi on the band structure remain largely independent, a robust conclusion we find to be valid even in the presence of significant alloy disorder where N and Bi atoms share common Ga nearest neighbours. Our calculations reveal that N-(Bi-) related alloy disorder strongly influences the conduction (valence) band edge states, leading in QWs to strong carrier localisation, as well as inhomogeneous broadening and modification of the conventional selection rules for optical transitions. Our analysis provides detailed insight into key properties and trends in this unusual material system, and enables quantitative evaluation of the potential of GaNyAs1−x−yBix alloys for applications in photonic and photovoltaic devices. arXiv:1712.07693v2 [cond-mat.mtrl-sci]

Towards low-loss telecom-wavelength photonic devices by designing GaBixAs1−x/GaAs core–shell nanowires

“…The small or zero thickness of the GaAs shell for ρ D ≥ 0.8 results in a weak quantum confinement effect along the growth direction, and therefore the spatial distributions of the electron wave functions become more localised in the in-plane directions.The spatial distribution of the hole wave functions is quite different from the electron wave functions and is governed by three effects: quantum confinement, biaxial strain and alloy disorder. As shown in the previous studies for the GaBi x As 1−x /GaAs quantum wells [32,44,51], the impact of the alloy disorder is dominant on the hole wave function confinements which is also evident in our study of nanowires. Overall, we conclude that the strong alloy disorder impact dominates the effects of the quantum confinement and strain, and leads to highly confined hole wave functions as shown in Figure 3.…”

“…We note that this work is focused on the GaBi x As 1−x material, however other bismide materials such as GaP 1−x Bi x , In x Ga 1−x Bi y As 1−y , and GaBi x N y As 1−x−y have also exhibited similar promising band structure properties based on the published bulk and quantum well studies [23,32,61,63,64].…”

“…Consequently, the results reported in this work not only provide a highly reliable fundamental understanding of the GaBi x As 1−x /GaAs nanowire properties, but also highlight a set of optimal parameters for the design of low-loss telecom-wavelength photonic devices, which can be expected to provide a clear direction for the future experiments on the fabrication of the bismide nanowires.This work is based on a systematic set of simulations in which the physical parameters of the GaBi x As 1−x /GaAs core-shell nanowires such as the relative diameters of the core and shell regions, the Bi composition of the core region, and the length of the nanowire are varied and their impact on the resulting optoelectronic character is delineated. The GaBi x As 1−x material has shown to exhibit a strong alloy disorder effect on its electronic properties [32,[42][43][44], which cannot be captured by the traditional effective-mass or k · p modelling techniques [45,46]. Here, we have applied atomistic simulations to quantitatively capture the impact of the random placements of the Bi atoms in the GaBi x As 1−x alloy formation and provide an accurate understanding of the resultant inhomogeneous broadening of the bandgap wavelength.…”

“…The larger charge separation in the GaBi x As 1−x nanowires with ρ D ≥ 0.8 may lead to a higher carrier collection at the different ends of the nanowire region and hence improve the efficiency of the solar to electrical conversion. Given that there is currently a significant research interest in employing bismide materials to target 1 eV spectral range in the design of multi-junction photovoltaic devices [32,59,60], this insight could be a catalysis for the experimental efforts to explore GaBi x As 1−x nanowires in the future solar cell devices. Inter-band absorption strength.…”

Impact of stoichiometry and strain on Ge1−x Sn x alloys from first principles calculations

“…This approach, which is similar to the computation of the spectral function at a single k-point employed in popular zone unfolding schemes, enables the evolution of both the energy and character of the alloy band edge states to be identified and tracked (see, e.g., Ref. 77).…”