18 Brovman and Kagan (see Ref. 17) have argued that the nonpairwise interactions between ions should be of short range. This is certainly borne out by the present force-constant analysis of the dispersion curves in A conclusive demonstration is presented that neutral donor capture, resulting in formation of the negative donor ion D", is the dominant electron capture mechanism in rc-type silicon samples of sufficiently low compensation in the liquidhelium temperature region. The capture-rate constant (and cross section) of this process, the lifetime of the D~ ion against recombination with D + ions, and the thermal ionization energy of the D" ion are determined for phosphorus, arsenic, and antimony donors. Separation of the contribution of D° electron capture from that of the D + "giant trap" 1 electron capture is effected by optically neutralizing the D* impurities with intrinsic radiation, 2 as well as by producing conduction and bound electrons of high spin polarization (P, to reduce the D° capture-rate constant. 3 The polarization dependence of the photocurrent which was formerly attributed to the mobility dependence associated with neutral impurity scattering 4 ' 5 in silicon of intermediate donor and low acceptor concentrations is shown to be due primarily to the D° capture mechanism, as in the case of low donor concentrations. 3 The negative-donorion concentration N(D") can be made comparable to or higher than the compensating impurity concentration, at modest illumination levels, and intrinsic illumination can thus strongly affect the charged impurity concentrations in a manner sim-Be. However, their theoretical justification has recently been criticized (see Ref. 16). 19 R. E. DeWames, T. Wolfram, and G. W. Lehman, Phys. Rev. 138, A717 (1965). 20 J. C. Gylden Houmann and R, M. Nicklow, Phys. Rev. B 1, 3943 (1970). 2 *R. M. Nicklow, N. Wakabayashi, and P. R. Vijayaraghavan, Phys. Rev. Be* , 1229 (1971). 22 Measurements are not available at the point K. However, the trends of the dispersion curves in that region suggest this sequence. ilar to that reported with intrinsic radiation. 2 The determination that the polarization dependence of the photocurrent arises primarily from D° capture rather than from neutral impurity scattering was implemented through the use of high magnetic fields up to 107 kOe, which permitted high polarizations to be attained over the entire liquid-helium temperature range. Hall-effect measurements in the polarized and unpolarized states confirm the conclusion. The reason that the neutral-impurity scattering mobility exhibits a much smaller (P dependence than predicted by the simple scaled theory 4 is not completely clear, but a plausible explanation is proposed.In Fig. 1 is shown the extrinsic photocurrent as a function of temperature for a phosphorus-doped silicon sample with low boron compensation [N(P) = 9.5xl0 15 cm" 3 , iV(B) = 4.2xl0 12 cm" 3 ]. 6 The currents were measured in a magnetic field of 35 kOe, and the squares and circles refer, respectively, to equilibrium (P val...
