Saturation of ionization edge absorption by donors in germanium

A study of saturation of the absorption and photoconductivity of Sb and P donors in Ge for radiation of 90 μm wavelength, i.e., of energy very closely above their ionization edges is presented at T=9.3 K. Under these conditions negligible heating by the excess radiation energy is expected, which provides a convenient opportunity to study the kinetics of photoionization and recombination. From these measurements we have determined the donor capture cross section of electrons at 9.3 K to be σc=(1.2±0.7)×10-12cm-2, and the relaxation time from the 2 s to the ground state as τ21=(5.8±1.0)×10-10s. The saturation intensity of the absorption coefficient is around three orders of magnitude higher than the saturation intensity of the photoconductivity. We explain the nonlinear photoconductivity by the Debye-Conwell dependence of the mobility on the number of photoionized donors and compensating acceptors. © 1993 Springer-Verlag.

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