Exciton resonance oscillator strength in doped CdS

Weak-compensated CdS:Cl monocrystal (1016-1018cm-3) was investigated at 5K. Oscillator strength was determined in experiments. It is shown that insular model enables to describe consistently the spectra of CdS:Cl reflection and transmission. Oscillator strengths are constant till metallization. However, different local levels of doping are realized in the crystal. This testifies to uneven character of oscillator strength dependence on doping level and to the jump of density of free carriers, when passing through the critical impurity concentration. The jump is related with change of coulomb interaction screening