Positron annihilation spectroscopy of vacancy-related defects in CdTe:Cl and CdZnTe:Ge at different stoichiometry deviations.

L Šedivý,E Belas,O Melikhova,R Grill,J Čížek

doi:10.1038/srep20641

L Šedivý, E Belas + Show 3 more

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https://doi.org/10.1038/srep20641

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Abstract

Positron annihilation spectroscopy (PAS) 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 as-grown crystals contain open-volume defects connected with Cd vacancies . 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. While annealing in Cd pressure reduces of the density, subsequent annealing in Te pressure restores . The CdTe:Cl contains negatively-charged shallow traps interpreted as Rydberg states of 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. Interpretation of the PAS data was successfully combined with electrical resistivity, Hall effect measurements and chemical analysis, and allowed us to determine the principal point defect densities.

Highlights

Interpretation of the Positron annihilation spectroscopy (PAS) data was successfully combined with electrical resistivity, Hall effect measurements and chemical analysis, and allowed us to determine the principal point defect densities
Positron annihilation spectroscopy (PAS) including Positron lifetime (LT) and Coincidence Doppler broadening (CDB) spectroscopy was usually used for the study of the structure of point defects in Cadmium telluride (CdTe)/Cadmium zinc telluride (CdZnTe) in the past13–18, but the link between defects and controlled annealing treatment has never been studied before
The as-grown CdTe:Cl and CdZnTe:Ge samples exhibit rather high resistivity, which is typical for the growth of Te-rich materials, where excess donors dominating above shallow acceptors are compensated by VCd8,42

Summary

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This work reports on an investigation of the influence of defined annealing in Cd or Te vapour on the defect structure of Cl-doped CdTe and Ge-doped CdZnTe semi-insulating single crystals. It is well known that LDA overestimates positron annihilation rates especially with d electrons and the lifetimes calculated within the LDA approach are often shorter than the values measured in experiment. This shortcoming is to some extend compensated when LDA approach is used with electron density constructed by ATSUP32,34. The GGA scheme is more sensitive to details of electronic structure than LDA30 and the lifetimes calculated using the GGA approach are it the best agreement with experiment when used with a self-consistent electron density For these reasons we performed self-consistent electron density calculations for selected positron states. The ATSUP-based approach describes well the high momentum part of the momentum distribution where the contribution of positrons annihilated by core electrons dominates. Positron state bulk VCd VCdTeCd VCdGeCd AC VCd2ClTe (VCd2ClTe) cluster (VCd2ClTe) cluster (VCd2ClTe) cluster

Results and Discussion

Eb kBT

Conclusions

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