Inclusions Elimination and Resistivity Restoration of CdTe:Cl Crystals by Two-Step Annealing

The aim of this work was to find an effective annealing treatment leading to a complete elimination of Te inclusions and simultaneously to conservation of the resistivity of CdTe:Cl crystals with varying chlorine doping level. This goal was reached by an application of two post-growth annealing steps. The first annealing step performed under Cd overpressure led to a significant reduction of Te inclusions. However, Cd-rich thermal treatment converted crystals into high-conductive n-types and re-annealing of the material in a Te atmosphere was necessary to restore the material resistivity. After application of the second annealing step under Te overpressure, resistivity higher than 10⁸ Ωcm was observed only in samples with high chlorine doping levels of n_Cl ≈ 2 × 10¹⁷ cm^-3. In addition, a new emission at 1.26 eV was observed in the photoluminescence spectra after two-step annealing. The size of Te inclusions, resistivity, photoluminescence spectra and detection properties of CdTe:Cl crystals before and after the two-step thermal treatment are discussed.