Electronic structure and Jahn–Teller effect in GaN:Mn and ZnS:Cr

Abstract

We present an ab initio and analytical study of the Jahn–Teller effect in two diluted magnetic semiconductorswith d4 impurities, namely Mn-doped GaN and Cr-doped ZnS. We show thatthe correct insulating electronic structure may be obtained by a propertreatment of the strong electron correlation in the 3d shell in combinationwith the Jahn–Teller distortion which breaks the local symmetry. Using theLSDA + U approach, we treat the zinc-blende and the wurtzite crystal structures of GaN:Mn, as wellas zinc-blende ZnS:Cr. We show that the trigonal distortion due to the wurtzitestructure is less important than the Jahn–Teller deformation. This observationallows us to construct a simplified phenomenological ligand field theory (trigonalinfluence is neglected) which completes the ab initio part. Our work corrects previousstudies and the obtained energy gain due to the Jahn–Teller effect (from both theLSDA + U calculation and the ligand field theory) is in good agreement with the experimental data.The same is true for the complete set of crystal field parameters obtained from thephenomenological model which agrees well with previous optical measurements.