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

• Published in: Scientific reports Vol. 9; no. 1; p. 6835
• Main Authors: Bushell, Zoe L., Broderick, Christopher A., Nattermann, Lukas, Joseph, Rita, Keddie, Joseph L., Rorison, Judy M., Volz, Kerstin, Sweeney, Stephen J.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 02.05.2019; Nature Publishing Group
• Subjects: 132/122; 639/301/119/1000; 639/301/119/995; Alloys; Humanities and Social Sciences; multidisciplinary; Science; Science (multidisciplinary); Splitting
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-019-43142-5

Using spectroscopic ellipsometry measurements on GaP 1− x Bi x /GaP epitaxial layers up to x  = 3.7% we observe a giant bowing of the direct band gap ( E g Γ ) and valence band spin-orbit splitting energy (Δ SO ). E g Γ (Δ SO ) 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 Δ SO in going from GaP to GaP 0.99 Bi 0.01 . The evolution of E g Γ and Δ SO 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 Γ and Δ SO with x . In contrast to the well-studied GaAs 1− x Bi x alloy , in GaP 1− x Bi x 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 Γ and Δ SO 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 GaP 1− x Bi x alloy band structure.