Chemical Splitting of Ground State of Lithium Donor in Silicon

Abstract

The energies of the ground states of the interstitial lithium donor in silicon have been calculated for interstitial T_d and D_3d site symmetries. It is shown that the assumption of the D_3d site symmetry for the lithium donor is favorable for the experimental fact of an “inverted” Group-V-like ground state. The lowest ground state is the 1s(A_2u+E_g+E_u) state with the ionization energy of 30 MeV, lying about 1.5 MeV below the 1s(A_1g) state. The corresponding observed values are 32.81 MeV and 1.8 MeV, respectively. It is shown that the “inverted” Group-V-like ground state is attributed to the orthogonalization effect to the core state of lithium in silicon and the interstitial nature of the lithium donor.