Defect levels in chromium-doped silicon

Abstract

The transient capacitance technique has been used to study the chromium-related levels in the silicon band gap. Chromium was diffused at temperature of 1100 and 1150°C for 0.5 and 3 hr. Five different levels at E c −0.11 eV, E c −0.21 eV, E c −0.28 eV, E c −0.36 eV and E c −0.45 eV were obtained from the Arrheniu plots of the electron thermal-emission rates. The number of levels in the upper half of the band gap decreased from five to two with an increase of Cr-diffusion period. Two levels were located at E c −0.20 eV (donor) and E c −0.43 eV (acceptor). A donor level was also observed at E v + 0.25 eV. The donor level was not affected by the diffusion condition. The majority carrier capture cross sections of the three dominant levels have been measured by the transient capacitance technique modified by the pulse transformer. The values were σ n = 4.1 × 10 −15 cm 2 for the upper donor at E c −0.20 eV, σ n = 2.0 × 10 −16 cm 2 for the acceptor at E c −0.43 eV and σ p = 9.1 × 10 −18 cm 2 for the lower donor at E v + 0.25 eV, and were independent of temperature. The three dominant levels are due to distinct chromium centers.