The effect of high injection on the density of states of silicon

The effects of high-injection levels on the conduction and valence bands of silicon have been determined according to theory based on first principles. The results show important narrowing of the energy gap by the injected electron-hole plasma as well as a reduction in the dopant-carrier interaction because of a reduction in the free-carrier screening radius. Interestingly, these two effects tend to compensate each other somewhat in heavily doped and heavily injected material. Since the gain of a bipolar device is very sensitive to the bandgap, device models need to include these effects in order to model a device correctly throughout its operating regime