Abstract
We present in this contribution results of two-step annealing, when the CdTe:Cl doped samples are at first annealed under Cd overpressure to remove inclusions and the re-annealed under Te overpressure to restore the high resistivity state. Investigation of samples after Cd rich annealing by infrared microscope has proven, that all inclusions are removed.
Also Te nano precipitates were strongly influenced by the annealing process. The resistivity of the samples after Te-rich annealing was restored to values (similar to 10(8)-10(9) Omega cm).
We observed, however, decrease of mobility-lifetime product of electrons from 10(-3)cm(2)/Vs to 10(-4)cm(2)/Vs. In order to understand the reason of this decrease we performed a study of point defects before and after annealing by thermoelectric effect spectroscopy.
It shows a decrease of concentrations of most deep levels after two-step annealing. This behavior is completely different compared to past annealing studies, where concentration of deep levels strongly increased after annealing.
The only level with an increased concentration in the current study is the midgap level (E similar to 0.8 eV). At the same time we observed increase of micro-twins in the samples investigated by transmission electron microscopy.
The decrease of charge collection efficiency after two-step annealing may be therefore connected with re-arrangement of near midgap levels due to increase of concentrations of structure defects (micro twins, dislocations) that accumulate in their surroundings point defects with energy similar to 0.75 eV.