The recent progress in formation of two-dimensional (2D) GaN by a migration-enhanced encapsulated technique  opens up new possibilities for group III-V 2D semiconductors with a band gap within the visible energy spectrum. The drawback of the planar monolayer GaN is its indirect band gap. Using first-principles calculations we explored alloying of 2D-GaN to achieve an optically active material with a tuneable band gap . The effect of isoelectronic III-V substitutional elements on the band gaps, band offsets, and spatial electron localization is studied using a set of first-principle assays [3,4]. In addition to optoelectronic properties, the formability of alloys is evaluated using impurity formation energies. A dilute highly-mismatched solid solution 2D-GaN:P features an efficient band gap reduction in combination with a moderate energy penalty associated with incorporation of phosphorous in 2D-GaN. The energy penalty is substantially lower than in the case of the bulk GaN. The group-V alloying elements also introduce significant disorder and localization at the valence band edge that facilitates direct band gap optical transitions thus implying the feasibility of using III-V alloys of 2D-GaN in light-emitting devices.
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