Anomalous low temperature ambipolar diffusion and Einstein relation.

The regular Einstein relation, connecting the coefficient of ambipolar diffusion and the Dember field with mobilities, is generalized for the case of an interacting electron-hole plasma. The calculations are presented for a nondegenerate plasma injected by light into semiconductors of silicon and germanium type. The Debye-Huckel correlation and the Wigner-Seitz exchange terms are considered. Corrections to the mobilities of carriers due to the difference between average and acting electric fields within the electron-hole plasma are taken into account. The deviation of the generalized relation from the regular Einstein relation is pronounced at low temperatures and can explain the anomaly of the coefficient of ambipolar diffusion, recently discovered experimentally.