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

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