Origins of band-gap renormalization in degenerately doped semiconductors

Degenerate n-type doping of semiconductors results in optical band-gap widening through occupation of the conduction band, which is partially offset by the so-called band-gap renormalization. From investigation of the magnitude and origin of these shifts through density-functional band-structure theory, we demonstrate that the key contribution to renormalization arises from the nonparabolic nature of the host conduction band but not the rigid shift of the band edges, as is the current paradigm. Furthermore, the carrier dependence of the band-gap widening is highly sensitive to the electronic states of the dopant ion, which can be involved in a significant reconstruction of the lower conduction band.