Theory of conduction band dispersion in dilute Bx Ga1-x As alloys

The conduction band structure of Bx Ga1-x As has a near-linear blueshift of the energy gap, which can be described using the virtual crystal approximation, but a dramatic increase in the band edge effective mass me* at low B composition, similar to that observed in Ga Nx As1-x. We use a tight-binding model to show that isolated B atoms have little effect either on the band gap or lowest conduction band dispersion in Bx Ga1-x As. In contrast, B pairs and clusters introduce defect levels close to the conduction band edge, which, through a weak band-anticrossing interaction, significantly reduce the band dispersion in and around the Γ point, thus accounting for the strong increase in me* and reduction in mobility observed in these alloys.