Giant bowing of the band gap and spin-orbit splitting energy in GaP1−xBix dilute bismide alloys

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Bushell, Zoe L.
Broderick, Christopher A.
Nattermann, Lukas
Joseph, Rita
Keddie, Joseph L.
Rorison, Judy M.
Volz, Kerstin
Sweeney, Stephen J.
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Using spectroscopic ellipsometry measurements on GaP1−xBix/GaP epitaxial layers up to x = 3.7% we observe a giant bowing of the direct band gap ($${E}_{g}^{{\rm{\Gamma }}}$$EgΓ) and valence band spin-orbit splitting energy (ΔSO). $${E}_{g}^{{\rm{\Gamma }}}$$EgΓ(ΔSO) is measured to decrease (increase) by approximately 200 meV (240 meV) with the incorporation of 1% Bi, corresponding to a greater than fourfold increase in ΔSO in going from GaP to GaP0.99Bi0.01. The evolution of $${E}_{g}^{{\rm{\Gamma }}}$$EgΓand ΔSO with x is characterised by strong, composition-dependent bowing. We demonstrate that a simple valence band-anticrossing model, parametrised directly from atomistic supercell calculations, quantitatively describes the measured evolution of $${E}_{g}^{{\rm{\Gamma }}}$$EgΓand ΔSO with x. In contrast to the well-studied GaAs1−xBix alloy, in GaP1−xBix substitutional Bi creates localised impurity states lying energetically within the GaP host matrix band gap. This leads to the emergence of an optically active band of Bi-hybridised states, accounting for the overall large bowing of $${E}_{g}^{{\rm{\Gamma }}}$$EgΓand ΔSO and in particular for the giant bowing observed for x ≲ 1%. Our analysis provides insight into the action of Bi as an isovalent impurity, and constitutes the first detailed experimental and theoretical analysis of the GaP1−xBix alloy band structure.
Spectroscopic ellipsometry measurements , Giant bowing , GaP1−xBix
Bushell, Z.L., Broderick, C.A., Nattermann, L., Joseph, R., Keddie, J.L., Rorison, J.M., Volz, K. and Sweeney, S.J. (2019). 'Giant bowing of the band gap and spin-orbit splitting energy in GaP 1− x Bi x dilute bismide alloys'. Scientific reports, 9(1), 6835. (8 pp). doi:10.1038/s41598-019-43142-5