The dissertation is devoted to a study of the electrophysical properties of CdTe crystals, both microdoped with Mn and crystals of Cd1-xMnxTe solid solutions, depending on the growth technology and the method of heat treatment.
The first section analyzes literary sources on the topic of dissertation. The electrophysical and optical properties of Cd-Mn-Te crystals are considered, structural defects in Cd1-xMnxTe crystals that arise during their growth/cooling were analyzed, and their detector characteristics were described.
The second section describes the technologies of crystals growth and experimental research techniques, used in the dissertation to study crystals of the Cd-Mn-Te system. The developed method of thermal annealing "dry zone" was described, which was used to purify the crystals from Te inclusions and from uncontrolled impurities.
The third section was devoted to the description and discussion of the results obtained for crystals of Cd1-xMnxTe solid solutions.
The first subsection shows the results of measuring the Hall coefficient. It was found that Cd1-xMnxTe crystals have an increased content of uncontrolled acceptors in comparison with Cd1-xZnxTe crystals. As a result of the application of the thermal treatment method "dry zone" to crystals Cd1-xMnxTe, the content of Te inclusions (up to 10 μm) was reduced by about an order of magnitude and the concentration of ionizing centers was reduced by ~ 3 times. Studies of the Hall effect and low-temperature photoluminescence confirmed that crystals that were first purified by the traveling heater method and then grown by the vertical Bridgman method had a high resistivity (ρ ~ 10 9-10 10 Ohm × cm) and were electrically uniform both along the length of the ingot. In the Cd0.9Mn0.1Te crystal at the concentration of the introduced impurity in indium C0 = 3.5 × 10 17 cm-3, a high degree of donor compensation, k>0.9, was achieved.
Crystals with a simultaneously high content of MnTe (Cd0.8Mn0.2Te, Cd0.7Mn0.3Te) and In (8×10 17 - 8×10 18 cm-3) very low electron mobility (μe <5 cm2/(c×s)), which was probably due to the deterioration of the microheterogeneity of the impurity-defect system due to the uneven dissolution of In in the crystal matrix. Hence, such crystals are unsuitable for practical use.
It was found that Ge-doped Cd1-xMnxTe crystals (x <0.1) (C0 = 8×10 18 cm-3) demonstrated a higher (by ~ 6 orders of magnitude) resistivity compared to undoped Cd1-xMnxTe crystals, as well as better macroscopic uniformity of electrical parameters. It was confirmed that the micro-inhomogeneity of electrical parameters in this material was weakly expressed, which, along with a high resistivity (ρ ~ 10 8-10 9 Ohm-cm), makes Cd1-xMnxTe-Ge crystals promising for their use as detectors.
The second subsection presents the results of high-temperature studies of the Hall effect in both undoped and In-doped Cd1-xMnxTe crystals. It was found that for a crystal with a low MnTe content (x = 0.02), the electron concentration dependence lines were ~ 1.5 times higher than for undoped CdTe, which indicates the presence of a donor point defect in the Cd0.98Mn0.02Te crystal most likely due to ionization Mn → MnCd+. For the Cd0.7Mn0.3Te crystal, decrease in the concentration of electrons at the pressure dependencies was observed, relative to CdTe, which was explained by a decrease in the solubility of the intrinsic donor interstitial Cdi2+ due to a decrease in the distances in the crystal lattice of Cd0.7Mn0.3Te.
The fourth section is devoted to the description and discussion of the results obtained for CdTe doped with Mn.
Positron annihilation spectroscopy in p-CdTe: Mn crystals revealed only one component of the positron lifetime. At the same time, in n-CdTe:Mn crystals, an increased value of VCd2- concentration was revealed from 1.5×10 16 to 6.5×10 16 cm-3, which indicated that donors of impurity (probably MnCd+) origin.
Using the results of high-temperature studies of the Hall effect and applying computer modeling of the spectrum of point defects in CdTe:Mn crystals, a system of quasi-chemical equations of defect formation was developed, and the obtained experimental dependences of the electron concentration were well described. Computer simulation confirmed the possibility of the existence in crystals of both single Mn and Mn-containing associates (MnCd+VCd2-)-. It was found that the solubility of Mn, even at high (T = 873 K) temperatures, is about ~ 1 × 1017 cm-3, and the ionization energy of MnCd+ Ed is ~ 100 meV. These features explain the resulting scatter in the values of the electrophysical parameters and the lack of correlation between them and the growing conditions, the doping scheme or the dopant concentration after cooling the Mn-doped CdTe crystals to ~ 300 K. Hence, it finally follows that Manganese is practically unsuitable for obtaining of CdTe:Mn crystals with reproducible electronic parameters at room temperatures.
