Observation of a shift of the mobility threshold in the D − band of silicon in an electric field according to the photoconductivity spectra

We have discovered that the extrinsic photoconductivity spectrum of doped, uncompensated crystalline Si at liquid-helium temperatures is qualitatively different in electric fields E above a critical value E _c . Specifically, the red edge of the photoconductivity, associated with photoionization of a neutral impurity, is shifted strongly to lower frequencies. This result is explained by the appearance of a mobility threshold in the D ⁻-band (upper Hubbard band) and the shift of this threshold as E increases. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 2, 89–94 (25 January 1996)