Properties of Gallium Selenide Doped with Sulfur
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Properties of Gallium Selenide Doped with Sulfur Valeriy G. Voevodin, Svetlana A. Bereznaya, Zoya V. Korotchenko, Aleksandr N. Morozov, Sergey Yu. Sarkisov, Nils C. Fernelius1, Jonathan T. Goldstein1 Siberian Physico-Technical Institute, 1 Revolution Sq. 634050, Tomsk, Russia 1 Air Force Research Laboratory, Materials & Manufacturing Directorate, AFRL/MLPSO Wright-Patterson Air Force Base, Dayton Ohio, 45433-7707, USA ABSTRACT This paper presents the results of investigations on the influence of sulfur doping on properties of gallium selenide crystals, grown by the Bridgman method from melts with sulfur content of 0.01-3 mass %, using the Hall effect, optical absorption, photoconductivity and microhardness measurements on GaSe:S. The results obtained are explained by assuming the formation of solid solutions of GaSxSe1-x and the presence of the competitive processes of point defects and structural disorder formation. INTRODUCTION Gallium selenide is one of the most promising materials for the mid-IR nonlinear optics. The basic merits of this material are: a broad transparency range 0.65-18 µm, a low optical absorption, a considerable nonlinear susceptibility, a high optical damage threshold, and the possibility of phase matching for some types of nonlinear optical conversions. The set of positive properties brings gallium selenede to the best five mid-IR nonlinear optics materials. [1] Laser technical development requires more and more perfect crystals. Because of this, there is a need to find new ways to improve gallium selenide properties. The doping of the crystals with isovalent impurities, in particular with sulfur, is one of the ways to improve optical and mechanical properties of gallium selenide. Along with the solution of technical problems with sample preparation, the characterization of the resulting crystals by different physical methods is important. In connection with this work, the electrical, optical and photoelectric properties of gallium selenide doped with sulfur were investigated. ELECTRICAL PROPERTIES The Hall effect measurements have shown the doping with sulfur did not considerably influence GaSe crystal electrical properties in the concentration range from 0.01 to 0.10.5 mass %. The hole type conductivity is preserved; the parameters lie within the range of values observed for samples cut from different parts of an ingot or different ingots of undoped gallium selenide (electrical conductivity 5⋅10-3-1⋅10-2 Ω-1cm-1, mobility 20-25 cm2V-1s-1, carrier concentration 1015-1016 cm-3, at 300 K). At sulfur concentrations of 1-3 mass % there is a noticeable decrease in the mobility (up to 3-9 cm2V-1s-1) and carrier concentration (up to 1⋅10-4 cm-3) and, as a result, a conductivity of the material (approximately up to 10-4 Ω-1cm-1) is observed (fig. 1-4).
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According to the existing literature data, one should expect a further decrease of these parameters with increasing sulfur concentration. The reduction of gallium selenide conductivity along the cleavage planes (001) with increasing
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