Annealing effects on defect levels of CdTe:Cl materials and the uniformity of the electrical properties

Abstract

CdTe crystals grown by the traveling heater method (THM) often show a pronounced nonuniformity along the ingots due to the thermal irregularities, the Te-excess growth conditions resulting from the retrograde slope of the solidus line of the phase diagram, and from the introduced impurities. In addition, structural defects can be present that influence the electrical and optical properties. The aim of this work is to study the annealing effects of Cl-doped CdTe on the uniformity of the material, the defects, the resistivity, the /spl mu//spl tau/ product, and on the detection properties. Samples have been annealed under various pressures (vacuum, argon, CdCl/sub 2/) and include different temperature stages between 250/spl deg/C and 850/spl deg/C. An increase of the resistivity was observed after a thermal treatment of these samples under argon pressure. In this case, the highest resistivity was obtained by annealing samples at 460/spl deg/C. The presence of CdCl/sub 2/ during the annealing leads to a better uniformity of the materials. The defects present in the materials have been investigated by photo-induced transient current spectroscopy (PICTS), thermo-electric emission spectroscopy (TEES), and thermally stimulated current (TSC) methods, which allow the calculation of their activation energy, their cross section, and their concentration.