Optical gain in GaN quantum wells with many-body effects

Band-gap renormalization and Coulomb enhancement due to many-body effects have been studied for wurtzite quantum well structures. Considering the coupling between the chemical potential and the band-gap renormalization, we calculated the band-gap redshifts of a few valence subbands self-consistently in a GaN/GaAlN quantum well structure using a nonparabolic band approach. We find that the renormalization not only produces redshift but also increases the quasi-Fermi-level separation relative to the effective band-gap. This causes an increase in optical gain for a given carrier density of about 40% compared with the free carrier model due to carrier redistribution by the band-gap renormalization similar to the enhancement by elastic stain. On the other hand, considering the angular dependence of the dipole matrix element, we have obtained an explicit expression for the Coulomb enhancement factor in wurtzite quantum well structures for the first time. Our results show that the band-gap renormalization is the dominant contribution to the optical gain enhancement rather than the “Coulomb/excitonic enhancement”in these structures.