Crystal structure and physical properties of GaSe single crystals annealed in sulfur atmosphere
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Crystal structure and physical properties of GaSe single crystals annealed in sulfur atmosphere Olga V. Voevodina, Aleksandr N. Morozov, Sergey Yu. Sarkisov Siberian Physico-Technical Institute 1 Novosobornaya sq. 634050, Tomsk, Russia Phone/ Fax: +7/3822/41-3636 Yuri M. Andreev Institute of Monitoring of Climatic and Ecological Systems SB RAS 10/3 Academicheskii Ave. 634055, Tomsk, Russia Nils C. Fernelius, Jonathan T. Goldstein Air Force Research Laboratory, Materials & Manufacturing Directorate, AFRL/MLPSO Wright-Patterson Air Force Base, Dayton Ohio, 45433-7707, USA ABSTRACT In spite of the progress in GaSe growing technology (high-quality crystals grown by the latest technology are characterized by low values of optical losses with the absorption coefficient values lying below 0.1 cm-1) the work continues on improving crystal properties for nonlinear optical applications. This paper presents the results of investigations on the influence of annealing in a sulfur atmosphere and in a vacuum on the properties GaSe single crystals, grown by the Bridgman method from the melt. The objective of this work was to study the possibility of intercalating GaSe with sulfur from the gas phase, and to compare the influence of doping with sulfur from melt and vapor phase on the structure and properties of GaSe crystals. Three series of annealing experiments have been conducted at temperatures 773, 923, 1073 K and the samples obtained have been studied by Hall effect, photoconductivity, optical absorption, microhardness measurements and X-ray diffractometry. The results obtained are explained by assuming the intercalating of sulfur to the interlayer space and substitution of Se with S. INTRODUCTION Gallium selenide remains one of the promising crystals for near and middle IR-range nonlinear optics. In addition, it has been shown that large high-quality GaSe crystals can be used for creation of millimeter and submillimeter (THz) coherent radiation sources [1]. In spite of it, additional advances in the crystal’s material properties are needed before GaSe achieves its full potential technological impact. Specifically, it is desirable that a method be found for increasing the crystal’s hardness, thereby reducing the crystal’s tendency to microspall. This would allow the crystal to be cut at angles arbitrarily related to the growth plane, in order to achieve higher optical conversion efficiency. Thus, the study of modifying the crystal properties by various doping and post-growth treatments is still an area of ongoing active research. Some investigations in this direction have already been performed [2, 3, 4]. The results show that the doping of the crystals with isovalent impurities is one of the possible ways of improving optical and mechanical properties of gallium selenide. Sulfur gives one of the most favorable modifications in crystal properties. In this connection to distinguish the changes of properties connected with sulfur, especially in the interlayer space, experiments on annealing in S vapor were conduct
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