Positron annihilation spectroscopy of defects in CdTe

Positron annihilation spectroscopy was used to examine the effect of defined Cd-rich and Te-rich annealing on point defects in Cl-doped CdTe and Ge-doped CdZnTe semi-insulating single crystals. The asgrown crystals contain open-volume defects connected with Cd vacancies (VCd ). It was found that the Cd vacancies agglomerate into clusters coupled with Cl in CdTe:Cl, and in CdZnTe:Ge they are coupled with Ge donors. The CdTe:Cl contains negatively-charged shallow traps interpreted as Rydberg states of (VCd ClTe )A-centres and representing the major positron trapping sites at low temperature. Positrons confined in the shallow traps exhibit lifetime which is shorter than the CdTe bulk lifetime; this is contrary to the common notion that shorter lifetimes of positrons occur in the bulk [2]. Interpretation of these experiments was successfully combined with electrical resistivity, Hall effect measurements and chemical analysis.

• [1] L. Šedivý et al., Sci. Rep. 6:20641 (2016). doi: 10.1038/srep20641.
• [2] K. Krause-Rehberg and H.S. Leipner, Positron Annihilation in Semiconductors, vol. 127 of Springer Series in Solid-State Sciences (1999).