Lifetime broadening of a parabolic band edge of a pure semiconductor at various temperatures

Abstract

In doped and in highly excited semiconductors many-body effects produce a shrinkage of the band gap. However, the Coulomb interactions between the conduction band electrons also cause a spreading of the conduction band edge and similar effects occur at the valence band edge. This effect is estimated here by considering the lifetime of an electron vacancy in the conduction band. Owing to the Coulomb interaction induced electron collisions (“Auger effect”) this lifetime is finite and broaders the state considered. The broadening is estimated theoretically for the simple model of a single parabolic band at non-zero temperature, and experimental evidence is presented from related studies showing that the effect can be observed. The spreading out of levels considered here corresponds to the imaginary part of the self energy (the real part is normally calculated as the main energy band narrowing). The results imply that under high excitation conditions the imaginary part can be a significant fraction of the real part.