Development of a new growth method of the semiconductor material CdTe, for obtaining imagers of X and gamma-ray

This thesis aims at obtaining large dimension CdTe crystals, suited to X and γ-rays detection, by a new method of growth using the evaporation of the solvent tellurium as the driving force for crystallization, from a tellurium-rich solution of cadmium and tellurium. This method is called Process By Solvent Evaporation (PBSE) or in French, Methode par Evaporation de Solvant. Two essential points characterize it: it is carried out in an open tube, which allows its extension to large diameters, and the growth proceeds at constant temperature, which must ensure a better uniformity of the properties of the elaborated material. The results obtained by this PBSE method show that the wafers can be classified in three categories (under-evaporated, ideal, over-evaporated) depending on the imposed 'temperature/time of growth' couple. It appears that only the wafers elaborated under the ideal conditions have properties required by the X and γ-ray detection. The characterization of several detectors extracted from various wafers made it possible to evaluate the potential of this material as detector for X and γ-rays: the material shows characteristics comparable to those indicated for various detectors in the scientific literature or present on the commercial market (in term of resolution and μτ product). The study of the chlorine incorporation by SIMS analysis shows that the chlorine profiles in the thickness of the various detectors are increasing from the beginning of growth face to the end of growth face according to an hyperbolic law. A simple and unidimensional model is developed to describe what occurs during a PBSE experiment. This model, based on the method of finished volumes, discretizes the liquid phase into several layers. According to the laws and numerical values assigned to the physical phenomena involved in the process, the model predicts the existence of three possible situations, which were encountered experimentally. (O.M.)