Photoionization cross sections in vanadium-doped silicon

Vanadium-doped silicon has been investigated using a photocapacitance method on n⁺-p and p⁺-n junctions. The photoionization cross-section spectra showed two levels at 0.47 eV below the conduction band and 0.485 eV above the valence band, and the complementary optical transition threshold energies were 0.665 and 0.77 eV, respectively. For the E _c-0.47-eV level, the electron photoionization cross section at the threshold energy depends significantly on temperature. This would be due to the photothermal ionization process via the excited states. For the E _v+0.485-eV level, the sum of the threshold energies in electron and hole emission processes was greater than the band gap. This indicates that phonon broadening due to lattice relaxation occurs in the photoionization spectrum. According to the configuration coordinate model, the local phonon energy and the lattice relaxation energy are approximately 350 K and 0.13 eV, respectively.