Far-infrared transmission measurements on P-doped Si at donor concentrations below the metal-insulator transition show absorption bands from donor pairs. We identify the lowest energy band as charge transfer excitations from a donor to its neigbhor, forming excitons (D+D-) in the Mott-Hubbard gap. The results suggest that charge transfer states in complexes dominate the low-energy optical excitations as the insulator approaches the Mott density.
All Science Journal Classification (ASJC) codes
- Condensed Matter Physics
- Materials Chemistry