Assignment of multiband luminescence due to the gallium vacancy-oxygen defect complex in GaN

TL;DR

This paper investigates how oxygen-related defect complexes in GaN cause multiband luminescence, including yellow emission, by combining quantum-mechanical and molecular-mechanical methods to analyze defect states and their optical properties.

Contribution

It introduces a hybrid QM/MM approach to study defect-induced luminescence in GaN, revealing the role of gallium vacancy-oxygen complexes in multiband emission.

Findings

Gallium vacancy-oxygen complexes lower vacancy formation energy in n-type GaN.

Defect levels remain within the band gap, affecting optical transitions.

Single defect centers can produce multiband luminescence signatures.

Abstract

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 band gap. We study the spectroscopy of this complex using a hybrid quantum-mechanical molecular-mechanical (QM/MM) embedded-crystal approach. We reveal how a single defect center can be responsible for multiband luminescence, including the ubiquitous yellow luminescence signature observed in n-type GaN, owing to the coexistence of diffuse (extended) and compact (localized) holes.