Chemical self-diffusion in undoped ZnS and in undoped CdSe

Chemical self-diffusion coefficients D(Δ) as a function of temperature T and metal (Zn or Cd) vapor pressure p_Zn or p_Cd has been studied in undoped ZnS and in undoped CdSe single crystals at high temperature. In the temperature range from 750 to 850 °C, D(Δ) in undoped ZnS can be described as D(Δ)=4.5×10⁻³ exp(−0.69 eV/kT) and in the temperature range from 1050 to 1150 °C, D(Δ) can be described as D(Δ)=1.2×10⁻⁴ exp(−0.43 eV/kT). The ZnS phase transition region is characterized by confused values of D(Δ) because of change due to mixture of phases. D(Δ) in ZnS and in CdSe is about three orders of magnitude faster than self-diffusion in these crystals in the same conditions. It was shown that the doubly ionized interstitial metal atoms are the dominanting diffusible defects in ZnS and in CdSe at high metal vapor pressure. D(Δ) is found to be almost independent on metal vapor pressure for undoped ZnS and for undoped CdSe at high p_Zn or p_Cd. In the temperature range from 565 to 700 °C, D(Δ) for CdSe can be expressed as D(Δ)=1.6×10⁻² exp(−0.41 eV/kT).