Valence band-anticrossing in GaP1−xBix dilute bismide alloys: giant bowing of the band gap and spin-orbit splitting energy

<p>Using spectroscopic ellipsometry measurements on GaP1&minus;xBix/GaP epitaxial layers up to&nbsp;x&nbsp;=&nbsp;3.7% we observe a giant bowing of the direct band gap (Eg&Gamma;) and valence band spin-orbit splitting energy (∆SO).&nbsp;Eg&Gamma;&nbsp;(∆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&nbsp;∆SO&nbsp;in going from GaP to GaP0.99Bi0.01. The evolution of&nbsp;Eg&Gamma;&nbsp;and&nbsp;∆SO&nbsp;with&nbsp;x&nbsp;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&nbsp;Eg&Gamma;&nbsp;and&nbsp;∆SO&nbsp;with&nbsp;x. In contrast to the well-studied GaAs1&minus;xBix&nbsp;alloy, in GaP1&minus;xBix&nbsp;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&nbsp;Eg&Gamma;&nbsp;and&nbsp;∆SO and in particular for the giant bowing observed for&nbsp;x &lt;=􏰁&nbsp;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&minus;xBix&nbsp;alloy band structure.</p> <p>&nbsp;</p> <p>&nbsp;</p>