Oxygen defects in Czochralski grown n-type silicon solar cell material were investigated with Fourier transform infrared spectroscopy (FTIR). Samples were annealed at fixed temperatures ranging from 300-470oC.
Different vibrational and electronic transition bands could be seen, like the VO2, VO3 and VO4 vibrational bands at room temperature measurements. The increase in VO3 band had a linear dependence with decreasing VO2 band throughout the annealing.
When oxygen rich silicon is annealed, thermal double donors (TDDs)appear in the material, which degrade the solar cell performance. Oxygen dimers are believed to be a precursor for TDDs and their vibrational bands at 556, 1012 and 1060 cm-1 were monitored by FTIR. The dimer concentration were found and showed an exponential dependency with annealing time. The activation energy was extracted by first order kinetics to be around 1.4-1.6 eV and assigned to the dimer diffusion with a diffusion pre-factor,D0, of 5.5E-3 - 5.0E-2 cm2/s.
After annealing, four point probe measurements were done and showed adecrease in resistivity, which means that the annealed samples had become more n-type, due to increase of TDD complexes.