Atomistic tight-binding study of electronic structure and interband optical transitions in GaBixAs1−x/GaAs quantum wells

Abstract

Original citationUsman, M. and O'Reilly, E. P. (2014) 'Atomistic tight-binding study of electronic structure and interband optical transitions inGaBixAs1−x/GaAs quantum wells', Applied Physics Letters, 104(7), pp.071103.

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.…”

“…This leads to an associated large broadening of the inter-band optical absorption wavelengths, known as the inhomogeneous broadening of the ground state transition. For the GaBi x As 1−x quantum well heterostructures, an inhomogeneous broadening of 23-33 meV has been reported in the literature [44,52]. As the inhomogeneous broadening of the optical transition wavelength plays an important role in the performance of optoelectronic devices [53], here we investigate its strength for the nanowire structures.…”

“…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 atomistic charge densities for the corresponding wave functions are visualised in realspace over the whole nanowire region by plotting red and cyan dots at the location of each atom, with the intensity of the color modulated by the strength of the charge density at that atomic sight (Figure 3 and 5 (c)). The inter-band optical transition strengths plotted in Figure 4 are computed by using the Fermi's golden rule [44].…”

Theory of the Electronic and Optical Properties of Dilute Bismide Quantum Well Lasers

“…In order to calculate the band structure of the GaBi x As 1−xbased QW laser structures we have introduced a 12-band k·p Hamiltonian for GaBi x As 1−x and related alloys [21], [32]. The 12-band model was derived on the basis of a tight-binding supercell model that has been successfully applied to study the electronic, optical and spin properties of GaBi x As 1−x alloys [16], [41], [42], [43]. The 12-band basis set explicitly includes the extended, spin-degenerate zone-center Bloch states related to the lowest conduction band (CB), as well as the lighthole (LH), heavy-hole (HH) and spin-split-off (SO) VBs of the GaAs host matrix.…”