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

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 (BiGa) and anionic (BiN) sites in Bi-incorporated GaN, as well as their complexes with native vacancies. Our calculations reveal that the charge-compensated (BiN+VGa)3− and (BiN+VGa)3+ defect complexes stabilize anionic bismuth incorporation, accounting for the experimentally observed absorption peaks at 0.86 and 2.95 eV. We further uncover the origins of the reported band edge emissions near 2.0 and 2.5 eV by examining various charge states of BiGa and BiN centers. We further show that Bi-related defects introduce deep mid-gap states that can act as efficient non-radiative recombination centers, potentially explaining the experimentally observed suppression of photoluminescence. Our findings elucidate the defect-level physics of Bi-doped GaN and provide practical guidelines for controlling the incorporation of Bi into GaN.