Giant bowing of the band gap and spin-orbit splitting energy in GaP_1-xBi_x dilute bismide alloys.

ABSTRACT: Using spectroscopic ellipsometry measurements on GaP_1-xBi_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_0.99Bi_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-xBi_x alloy_, in GaP_1-xBi_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-xBi_x alloy band structure.

SUBMITTER: Bushell ZL 

PROVIDER: S-EPMC6497675 | biostudies-literature | 2019 May

REPOSITORIES: biostudies-literature