Prediction of multiband luminescence due to the gallium vacancy–oxygen defect complex in GaN

Oxygen is the most common unintentional impurity found in GaN. We study the interaction between substitutional oxygen (ON) and the gallium vacancy (VGa) to form a point defect complex in GaN. The formation energy of the gallium vacancy is largely reduced in n-type GaN by complexing with oxygen, while thermodynamic and optical transition levels remain within the bandgap. We study the spectroscopy of this complex using a hybrid quantum-mechanical molecular-mechanical embedded-cluster approach. We reveal how a single defect center can be responsible for multiband luminescence, including possible contributions to the ubiquitous yellow luminescence signatures observed in n-type GaN, owing to the coexistence of diffuse (extended) and compact (localized) holes.