Thermal configurations of oxygen in silicon

The central position and the infrared absorption coefficient of the 9 m band of Si samples were measured with Fourier transform infrared spectroscopy (FTIR) at temperatures from T=77 K to 775 K. The infrared absorption coefficients were corrected by considering background absorption and free carrier absorption calculated from the increased free carrier concentration and from the resistivity determined from Hall effect measurements. We found the central position of the 9 m band to shift to longer wavelengths with increasing temperature. The concentration [O_i] of interstitial oxygen is almost constant for T<600 K, but decreased rapidly for T>600 K. These results verified there are two types of thermal configurations of oxygen in silicon: The bonded Si₂O configuration with a binding energy E_b0.8 to 1.0 eV at T77 K to 600 K, and the Si₂O configuration coexists with a quasi-free interstitial oxygen (QFIO) state for T>600 K. The lattice potential barrier E_L, which retards QFIO atoms from migrating in the lattice, is estimated to be 1.5 to 1.6 eV. From these configurations the anomalous diffusivity of oxygen in silicon can be explained quite well.