Crystals Cd 1-x ZnxTe – a promising material for non-cryogenic semiconductor detectors: preparations, structure defectness and electrophysical properties

Abstract

Among semiconductor materials with wide band gap, much attention has been paid to CdTe and Cd 1-x Zn x Te as roomtemperature detectors of X-ray and gamma-radiation. They have high atomic number (~ 50), high density (> 6 g/cm 3) and relatively high carrier mobility. It has been shown that formation of solid solutions CdTe-ZnTe is accompanied by broadening of the band gap, increase of resistivity (by more than an order of magnitude), and improved stability of spectral characteristics as compared with CdTe [1]. A general problem for semiconductor materials based on A II B VI compounds is the difficulty of growing structurally perfect crystals characterized by high degree of chemical purity and stoichiometry. Requirements to the structural perfectness of crystals Cd 1-x Zn x Te are very high, because practically all their principal electrophysical and optical characteristics are strongly structure-dependent. The present work was focussed on studying effects of preparation conditions of crystals Cd 1-x Zn x Te upon concentration of electrically active structural defects in this material and X-ray sensitivity of detectors made on its base. 2. Experimental procedure We studied a set of crystals Cd 1-x Zn x Te (32 mm in diameter) grown by Bridgman method in vertical compression furnaces under inert gas (argon) pressure from 3.5 to 5.5 MPa. Crystal growth regimes are presented in Table 1. In this work, crystals Cd 1-x Zn x Te were grown using raw materials pre-synthesized in a quartz ampoule, as well as those synthesized from elements (Cd,Zn,Te) directly in the growth equipment. During growth of certain crystals (No. 9-12) gas samples were taken to analyze concentration of oxygen-containing impurities in the atmosphere of the growth furnace. Carbon oxide content at different growth stages varied from 0.1 to 3 vol. %. Concentration of oxygen and water vapor in the initial argon did not exceed 1⋅10-3 vol. %. It could be concluded that in the growth furnace carbon oxide was formed from the air desorbed from the construction material, and its removal was necessary. Quality and uniformity of the properties and structure of the grown crystals was determined by several independent

Cadmium Refining in Chloride Melts Using a Bipolar-Electrode Electrolyzer

“…Note that, in the spectral range corresponding to the formation of Cd 2 2+ and Cd 2 3+ cations, the absorbance of the reaction mixture as a function of Cd m x+ content obeys the Bouguer-Lambert-Beer law (Figure 3). This finding suggests that, measuring the absorbance as a function of time, one can spectroscopically follow the kinetics of Cd 2 2+ and Cd 2 3+ formation according to schemes [3] and [4]. 3+ concentrations upon the formation of the corresponding complex cations.…”

“…The absorption spectra in Figure 2 show a shoulder at about 335 nm, which may be due to the reaction Cd + + Cd 2+ = Cd 2 3+. [4] According to Ershov (26), in concentrated aqueous solutions Cd + reacts with Cd 2+ to form Cd 2 3+ clusters. Note that, in the spectral range corresponding to the formation of Cd 2 2+ and Cd 2 3+ cations, the absorbance of the reaction mixture as a function of Cd m x+ content obeys the Bouguer-Lambert-Beer law (Figure 3).…”

“…At j = 0.05 А/сm 2 , the oxidation state of cadmium is 2+, which confirms that the electrode process involves two electrons. With increasing current density, the oxidation state of cadmium decreases, which attests to the formation of subvalent cadmium compounds by reactions [3], [4], and [10].…”

“…High-purity cadmium is one of the starting materials for the synthesis of II -VI compound semiconductors (1,2) and CdTe-CdS, Cd 1-x Zn n Te, Cd x Hg 1-x-y Zn y Te solid solutions them (3)(4)(5), which find application in opto-and microelectronics. In addition, high-purity cadmium is used in the fabrication of light-emitting diodes [6], solar cells (7,8), and detectors based on wide -gap semiconductors CdTe and CdZnTe of radiation monitoring at nuclear power plants (9).…”