Positron trapping at divacancies in thin polycrystalline CdTe films deposited on glass

We have performed positron annihilation experiments on CdTe films grown by vacuum evaporation at 220°C on both plain glass and indium-tin-oxide-coated glass substrates. By checking the linearity of the valence annihilation parameter S versus the core annihilation parameter W we introduce a method to analyze the data which directly shows that the same vacancy defect can be present in all the films. By comparing the core annihilation parameter at the defect to that at the V_Cd vacancy we can identify this defect as the divacancy V_Cd-V_Te. Its concentration in the films decreases from about 10¹⁸ to less than 10¹⁶ cm ^-3 after annealing in air at 400°C for about 30 min. Chlorine doping seems to stabilize the divacancies.