Electronic structure and defect properties of Bi-doped GaN: origins of photoluminescence and optical absorption

TL;DR

This study uses hybrid density functional theory to investigate defect-related optical properties in Bi-doped GaN, revealing defect complexes responsible for specific absorption and emission features, and offering insights for material control.

Contribution

It provides the first systematic theoretical analysis of defect-related optical phenomena in Bi-incorporated GaN, clarifying the origins of observed photoluminescence and absorption peaks.

Findings

Identification of defect complexes responsible for absorption peaks at ~1.11 eV and ~3.17 eV.

Explanation of band-edge emissions near 2.0 eV and 2.5 eV based on defect charge states.

Guidelines for controlling Bi incorporation in GaN based on defect physics.

Abstract

Extreme lattice-mismatched III-V nitrides, such as Bi-incorporated GaN, have been realized experimentally thanks to recent advances in epitaxial growth and characterization techniques. However, theoretical insights into defect-related optical absorption and emission phenomena in these materials remain scarce. Here, we apply hybrid density functional theory to systematically explore the role of substitutional bismuth atoms on both cationic $\mathrm{Bi_{Ga}}$ and anionic $\mathrm{Bi_{N}}$ sites in Bi-incorporated GaN, as well as their complexes with native vacancies. Our calculations reveal that the charge-compensated defect complexes $(\mathrm{Bi_{N}} + \mathrm{V_{Ga}})^{3-}$ and $(\mathrm{Bi_{N}} + \mathrm{V_{Ga}})^{3+}$ stabilize anionic bismuth incorporation, accounting for the experimentally observed absorption peaks at ~1.11 eV and ~3.17 eV. We further uncover the origins of the reported band-edge emissions near 2.0 eV and 2.5 eV by examining various charge states of $\mathrm{Bi_{Ga}}$ and $\mathrm{Bi_{N}}$ centers. Our findings elucidate the defect-level physics of Bi-doped GaN and provide practical guidelines for controlling the incorporation of Bi into GaN.