Incorporation of Boron in Gallium Nitride*

Ternary alloys of the group-III nitrides are integral in the design of electronic and optoelectronic devices. To extend the capabilities of these alloys, boron-containing nitride alloys, such as B_xGa_1-xN (BGaN), are being considered. Boron nitride, however, is most stable in the hexagonal phase, unlike GaN which is stable in the wurtzite phase. As such, there is a lack of experimental information on the properties of wurtzite-phase boron-containing alloys. Using first-principles calculations with a hybrid functional, we explore the nature of boron incorporation in GaN. In the dilute limit, we consider substitutional and interstitial incorporation of boron. We also study the change in the electronic structure of GaN with increasing boron concentration. Wurtzite BN has an indirect band gap, while GaN has a direct band gap. We investigate the direct and indirect nature of the alloy band gap using a projection scheme and by calculating dipole matrix elements. We find that the fundamental band gap of BGaN is direct for boron concentrations below 50%. The large band-gap bowing results in a fundamental band gap that is effectively unchanged from the GaN band gap for a wide range of B concentrations.