Study of band-gap shrinkage in cinnabar (α-HgS) by cathodoluminescence under very strong excitation

The effects of a very strong excitation on the edge luminescence of α-HgS are studied. Characteristic modifications are observed (emission peak shift towards low energy, broadening of the spectrum). The emission peak shift is interpreted in terms of a band-gap shrinkage by interaction between free carriers. The state density of the conduction band is calculated, as well as the Fermi quasi-level of the electrons. Since the semiconductor is degenerate at the excitations used, the absence of a Burstein shift leads to the assumption that the radiative transitions have their origin in the bottom of the conduction band.