The conduction band structure of ${\mathrm{B}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ 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 $\mathrm{Ga}{\mathrm{N}}_x{\mathrm{As}}_{1-x}$. 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 ${\mathrm{B}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$. 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 $\Gamma$ point, thus accounting for the strong increase in $m_e^{*}$ and reduction in mobility observed in these alloys.

• Received 13 June 2007

DOI:https://doi.org/10.1103/PhysRevB.76.075210