Surface tension of Cd0.9Zn0.1Te melt
Graphical abstract
Introduction
Zinc-cadmium telluride is a wide-gap material applied in semiconductor ionizing radiation detectors operating at room temperature [1], [2] in medical equipment, devices for environmental monitoring, high-resolution X-ray and gamma spectrometers [3], [4], [5], [6], [7], [8], [9]. Since crystals are usually grown from melt [10], [11], [12], the data on properties of this material in the liquid state are required for the development and optimization of crystal growth. The crucial role of Te inclusions in detectors’ performance of melt grown Cd1-xZnxTe (CZT) crystals is substantiated in many works [13]. Modeling of CZT Bridgman crystal growth under steady conditions or rotation schedule reveals the effects of Te segregation and transport depending on cooling conditions [14]. Morphology, density and distribution of Te inclusions in CZT crystals grown by Bridgman and traveling heater method are experimentally studied in [15]. All these studies highlight the impact of cooling on crystal perfection and distribution of impurities. In this view the surface tension of melt is an indispensable characteristic of solidification.
Measuring of the surface tension of metal liquids is widely used to analyze and develop solidification process [16]. These studies are not least important for semiconductors. However, information on the surface tension of AIIBVI melts is scarce [17]. In liquid metals, the surface tension is a function of the oxygen which acts as surface-active element. Oxygen adsorption leads to decrease in surface tension of metals [16]. Since Cd1-xZnxTe crystals are grown from melt in inert gas atmosphere, argon adsorption on the interface should have an impact on the surface tension. In the present work stalagmometric method designed for real conditions of AIIBVI crystal growth by vertical zone melting was applied for the first time to measure surface tension of the Cd0.9Zn0.1Te melt as a function of argon pressure. Solubility of argon gas in adsorption layer of the liquid was found.
Section snippets
Experimental
The stalagmometric method is based on measuring the weight of a drop falling from a capillary. An experimental setup for measuring the surface tension of melt is schematically shown in Fig. 1.
The stalagmometer was made of graphite that can withstand high temperatures and does not interact with the melt. The experiments were carried out in argon atmosphere like in [1], [18], [19].
In the course of the experiments, the previously synthesized zinc-cadmium telluride was
Results and discussion.
Fig. 2 shows a solidified drop of melt obtained in the experiment, used to measure the surface tension at argon pressure of 7 MPa.
The drops were weighed and their average weight was determined aswhere n is the number of droplets formed in one experiment.
The surface tension of the melt was calculated by the following equation [20]:where g is the free fall acceleration, r is the capillary radius, k is the constant of the stalagmometer.
The stalagmometer constant was
Conclusions
The surface tension of the melt was experimentally found to decrease as argon pressure increased from 2 to 9 MPa. The experimental results comply with the Shishkovsky equation. Using the coefficients of the Shishkovsky equation obtained from the experimental data, the concentration of impurity atoms in the melt per unit area on the surface, as well as per gas molar volume in the adsorption layer is calculated.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was supported by the Ministry of Science and Higher Education of Russia (grant No. 075-15-2021-1362, contract No. 8418.21.11).
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