Compensation processes in CdTe-based compounds

The compensation process in semi-insulating CdTe-based compounds is known to be related to the interaction among shallow and deep levels induced by impurities, grown-in lattice defects and by their complexes. We have carried out Photo-Induced Current Transient Spectroscopy (PICTS) and Photo-Deep Levels Transients Spectroscopy (P-DLTS) analyzes together with DLTS analyzes to investigate the role that acceptors and donors play in the compensation mechanism. To this purpose we have compared semi-insulating materials with different stoichiometry and different resistivity, i.e., with different free carrier concentration. We have examined also semiconducting material in order to compare extrinsically compensated and self-compensated CdTe-compounds. Our attention has been focused on the deep levels close to midgap in order to deepen our understanding of their behavior as a function of the position of the Fermi level since they are critical for the compensation process. We have achieved experimental evidence that in Cd_(1-x)Zn_xTe the level H at E_V+0.75 eV has a donor-like character. The possible extension of the donor-like character of this defect to CdTe:Cl should be positively considered albeit it can not be assessed by the present investigation.