Dependence of the Sn0/2+ charge state on the Fermi level in semi-insulating CdTe

We explored the growth and characteristics of CdTe doped with Sn to heighten our understanding of the role of deep levels on electrical compensation and trapping. We demonstrated, for the first time, the strong dependence of the Sn-Cd charge state on the Fermi-level variation (2-3kT) in high-resistivity CdTe. The concentration of deep traps for electrons was determined by the number of doubly positively charged Sn2+ atoms. Thermoelectric-effect spectroscopy and photovoltage measurements revealed the conversion of the SnCd defect from the electron Sn-Cd(2+) trap to the hole Sn-Cd(0) trap. The results agree well with the existence of a negative U-center in the Sn-Cd(0/2+) defect. We also showed that the neutral Sn defect is responsible for the near midgap C-band -> bound hole radiative transitions band with a maximum at 0.76 eV.