The microscopic structure of DX centers in Cd 0.8Zn 0.2Te:Cl

Abstract

The microscopic structure of chlorine DX centers was studied in Cd0.8Zn0.2Te:Cl by positron annihilation and thermoelectric current measurements. Photoexcitation of the DX centers induces a transition of the Cl atoms to the shallow-donor state and persistent photoconductivity (PPC) at low temperature. The DX state is recovered by annealing at 140 K where the relaxation of the substitutional Cl atoms to the DX state was observed. The shallow-deep transition is coincident with a sharp decrease of the positron line-shape parameter and a significant increase of annihilation with high-momentum core electrons. The results indicate positron trapping and annihilation at chlorine A centers after photoexcitation and at DX centers after annealing. Among the three configurations proposed for Cl DX centers in Cd 1-xZn xTe the data support the bond-breaking geometry and the relaxation of the Cl and Cd(Zn) atoms along the [111] direction. The thermal barrier for the shallow-deep transition was found to be 0.44 eV.