Giant bowing of the band gap and spin-orbit splitting energy in GaP(1−x)Bi(x) dilute bismide alloys

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 ([Formula: see text] ) and valence band spin-orbit splitting energy (Δ(SO)). [Formula: see text] (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 [Formula: see text] 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 [Formula: see text] 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 [Formula: see text] 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.