RADIATIVE SPECTRA FROM SHALLOW DONOR-ACCEPTOR ELECTRON TRANSFER IN SILICON

Radiation associated with shallow donor-acceptor electron transfer in silicon has been examined in the liquid-helium temperature region for various combinations of group-V donors and group-III acceptors. The spectra for all impurities are quite similar, exhibiting TA- and TO-phonon-assisted lines, as well as a no-phonon line in all but the (Sb,B)-doped sample. A (P,In) sample exhibits an unusual extra line which is attributed to an LA-phonon-assisted transition. A theory analogous to that of Thomas, Hopfield, and Augustyniak, modified to take account of anisotropic donor wave functions, is used to analyze the line shapes and determine rate constants and the impurity-pair Coulomb energy for pairs that decay at different times after impurity neutralization. This leads to a direct measurement of the indirect silicon energy gap of 1.166±0.0010 eV and an exciton binding energy of 0.0102±0.0015 eV, when combined with infrared-absorption measurements near the indirect gap. The analysis also indicates that optically determined impurity ionization energies are correct, and that the thermally determined impurity activation energies and their concentration dependence probably result from carrier redistribution effects rather than modification of the impurity ionization energies of the majority of the impurities. © 1969 The American Physical Society.