Structural and electronic properties of wurtzite B_<i>x</i>Al_1–<i>x</i>N from first‐principles calculations

Abstract

The structural and electronic properties of wurtzite B x Al 1− x N (0 ≤ x ≤ 1) are studied using density functional theory. The change of lattice parameters with increased B composition shows small bowing parameters and thus slightly nonlinearity. The bandgap exhibits strong dependence on the B composition, where transition from direct to indirect bandgap occurs at a relatively low B composition ( x ∼ 0.12) is observed, above which the bandgap of B x Al 1− x N maintained indirect, thus desirable for low‐absorption optical structures. The Γ v ‐ A c and Γ v ‐ K c indirect bandgaps are dominant at lower and higher B compositions, respectively. Density of states (DOS) of the valence band is susceptible to the B incorporation. Strong hybridization of Al, B, and N in p‐states leads to high DOS near the valence band maximum. The hybridization of Al and B in s‐states at lower B compositions and p‐states of B at higher B compositions give rise to high DOS near lower end of the upper valence band. Charge density analysis reveals the B‐N chemical bond is more covalent than the Al‐N bond. This will lead to more covalent crystal with increasing B composition. Dramatic change of the heavy hole effective mass is found due to significant curvature increase of the band by minor B incorporation.