Radiative Recombination and Equilibrium between Near‐Band‐Edge Tail States in n‐Type GaAs Available to Purchase

The detailed balance method of deriving the radiative‐recombination coefficient in semiconductors from the absorption curve is strictly applicable only when thermal quasiequilibrium exists for the carriers within each band. It is shown here that in many cases when the bands tail into the gap, the carriers are not in thermal equilibrium within the tail, even quite near the band edge, and that the detailed balance method requires modification. A simplified model, that of a regional bandgap variation, is suggested as an approximation to the complex band‐tailing situation. It is applied to measurements of photoluminescence and absorption in n‐type GaAs, of varying degrees of degeneracy, and values of the recombination constants at 296° and 77°K are derived. They are of the same magnitude as those in ideal material with no tailing. An uncertainty arises in degenerate material since it is not clear whether the reduced values of Burstein shift observed are entirely attributable to band shrinkage. The contribution of the deeper tail states to the luminescence often appears to be approximately independent of the separation of the state from the band edge.