Rare-earth defects in GaN: A systematic investigation of the lanthanide series

Abstract

Rare-earth (RE) doped GaN is of interest for optoelectronics and spintronics and potentially for quantum applications. A fundamental understanding of the interaction between RE dopants and the semiconductor host is key to realizing the material's full potential. This work reports an investigation of lanthanide (Ln) defects in GaN using hybrid density-functional defect calculations. We find that all the Ln dopants incorporated at the Ga lattice site, LnGa (Ln = La-Lu), are stable as trivalent ions, but Eu and Yb can also be stabilized as divalent and Ce, Pr, and Tb as tetravalent. The location of Ln-related defect energy levels and of the Ln 4f states in the energy spectrum of the host material is determined from first principles. We elucidate the interplay between defect formation and electronic structure, including the Ln-N interaction, and the effect of doping on the local lattice environment. Optical properties are investigated by considering possible band-to-defect and defect-to-band transitions involving the LnGa defects. These "charge-transfer" transitions result in broad absorption and emission bands which likely impact the performance of the material.