The energy positions of the optical transitions in both GaN and ZnO were investigated when the samples were excited simultaneously with a HeCd laser and an Ar+ ion laser. The increased number of free electrons excited by the Ar+ ion laser will effectively screen both the free exciton and bound exciton transitions, resulting in a blueshift. The increased number of free electrons also produces many-body effects, which lead to a reduction of the band gap energy and thus a redshift. The resultant of screening and renormalization results in a redshift of the optical transitions in ZnO but a nearly vanishing shift in GaN.
Reynolds, D. C.,
Look, D. C.,
& Jogai, B.
(2000). Combined Effects of Screening and Band Gap Renormalization on the Energy of Optical Transitions in ZnO and GaN. Journal of Applied Physics, 88 (10), 5760-5763.