Optical pumping NMR in the compensated semiconductor InP:Fe -: art. no. 075215

The optical pumping nuclear-magnetic-resonance effect in the compensated semiconductor InP:Fe has been investigated in terms of the dependences of photon energy E-p, helicity sigma(+/-), and exposure time tau(L) of infrared lights. The P-31 and In-115 signal enhancements show large sigma(+/-) asymmetries and anomalous oscillations as a function of E-p. We find that (i) the oscillation period as a function of E-p is similar for P-31 and In-115 and almost field independent in spite of significant reduction of the enhancement in higher fields. (ii) A characteristic time for buildup of the P-31 polarization under the light exposure shows strong E-p dependence, but is almost independent of sigma(+/-). (iii) The buildup times for P-31 and In-115 are of the same order (10(3) s), although the spin-lattice relaxation times T-1 are different by more than three orders of magnitude between them. The results are discussed in terms of (1) discrete energy spectra due to donor-acceptor pairs in compensated semiconductors and (2) interplay between P-31 and dipolar ordered indium nuclei, which are optically induced.