Compensation processes in CdTe-based compounds

The compensation 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 PICTS (Photo-Induced Current Transient Spectroscopy) and P-DLTS (Photo-Deep Levels Transients Spectroscopy) analyses together with DLTS analyses 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 behaviour 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_x Te 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 assessed by the present investigation