Electron Spin Resonance Experiments on Donors in Silicon. I. Electronic Structure of Donors by the Electron Nuclear Double Resonance Technique

The ground-state wave function of the antimony, phosphorus, and arsenic impurities in silicon has been investigated by means of the electron nuclear double resonance (ENDOR) method. By this method the hyperfine interactions of the donor electron with the Si^29 nuclei situated at different lattice sites were obtained. The isotropic part of the hyperfine interaction agreed with the theory of Kohn and Luttinger to better than 50%. From a comparison of the experimental results with their theory a value for the conduction band minimum in silicon of k₀{k₌₀ₗ}=0. 850. 03 was obtained. So far no satisfactory theory exists to account quantitatively for the observed anisotropic part of the hyperfine interaction. The observed line shape agreed with the shape predicted by summing up the individual hyperfine interactions which are the cause of the broadening. The behavior of an inhomogeneously broadened line observed under adiabatic fast passage conditions is discussed in an appendix. The electronic g-values were measured with respect to the free carriers in a degenerate n-type silicon sample. The g-value of the free carriers was found to be 1. 998750. 00010. The deviations of the donor g-values from the above value is several parts in 10^4 and increases monotonically with increasing ionization energy of the donors. Besides the shallow donors Sb, P, and As, several other centers were investigated, but in considerably less detail. They include the chemical impurities Bi, Li, Fe, centers associated with the surface of the sample and with the heat treatment of silicon. The influence of substitutional germanium atoms on the resonance line in phosphorus-doped silicon has also been investigated.