Effect of the Working Gas Pressure on the Structure of ZnO Layers
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Effect of the Working Gas Pressure on the Structure of ZnO Layers A. Kh. Abdueva,*, A. K. Akhmedova, A. Sh. Asvarova,b, A. E. Muslimovb, and V. M. Kanevskyb a Amirkhanov
Institute of Physics, Dagestan Federal Research Center, Russian Academy of Sciences, Makhachkala, 367030 Russia b Shubnikov Institute of Crystallography, Federal Research Center “Crystallography and Photonics,” Russian Academy of Sciences, Moscow, 119333 Russia *e-mail: [email protected] Received April 14, 2020; revised May 7, 2020; accepted May 12, 2020
Abstract—Zinc oxide layers have been synthesized by magnetron sputtering of ZnO:Ga ceramic and ZnO:Ga + 10 wt % Zn cermet targets in an Ar atmosphere and by reactive sputtering of a zinc target in an Ar–O2 atmosphere. The effect of working gas pressure in the chamber on the growth and structure of ZnO layers has been studied. It has been established that, for all the target types used, the crystal structure of ZnO nanocrystallites forming the layer improves with an increase in working gas pressure. The effect of excess zinc in the reagent flow on the microstructure and properties of the ZnO layers has been analyzed by comparing the electron microscopy and X-ray diffraction data on the layers formed by sputtering targets of different types. DOI: 10.1134/S1063774520060024
INTRODUCTION Functional layers based on zinc oxide are widely used in various optoelectronic applications, e.g., in information display systems, thin-film solar energy converters, and light-emitting structures. At present, the main commercial method for synthesizing functional layers based on zinc oxide is magnetron sputtering. Long-term investigations in this field made it possible to establish the entire set of factors acting during magnetron deposition of layers, among which the key one is the growth surface temperature. However, the recent trend toward the transition to polymer carriers imposes serious restrictions on the growth temperature of layers [1]. In the low-temperature synthesis, the interaction of sputtered atoms in the vapor phase comes to the foreground. Under certain conditions, this interaction may lead to vapor-phase clustering of the reagent flow with formation of fractal dendritic structures on the substrate [2–7]. In this case, the structural quality of layers significantly degrades. At the same time, disordered layers with a large specific surface area are of certain interest for designing gas sensors, Grätzel cells, and supercapacitors [8, 9]. In some works, various factors leading to the reagent flow clustering have been discussed. In particular, Bouaraba et al. [10] demonstrated a pronounced effect of working gas pressure on the energies of particles reaching the growth surface. In [11, 12], the processes leading to gas-phase clustering of metal vapor during magnetron sputtering were considered.
Another possible factor affecting the structure of low-temperature magnetron layers is the variation in growth surface temperature during deposition [13, 14]. For instance, it was noted in [15]
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