Theory of conduction band dispersion in diluteBxGa1−xAsalloys

Abstract

The conduction band structure of ${\mathrm{B}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ 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 ${m}_{e}^{*}$ at low B composition, similar to that observed in $\mathrm{Ga}{\mathrm{N}}_{x}{\mathrm{As}}_{1\ensuremath{-}x}$. 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 ${\mathrm{B}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$. 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 $\ensuremath{\Gamma}$ point, thus accounting for the strong increase in ${m}_{e}^{*}$ and reduction in mobility observed in these alloys.