In this paper the optical and photoelectrical properties of CdS x Se 1-x films prepared using the screenprinting and sintering technique, were studied. CdCl 2 was used both as a sintering flux and as a doping agent. CuCl was also used as a doping agent. The temperatures and times of preparation varied in the range of 500 -600 °С and 5 -60 min, respectively. The as-prepared films were characterized by the scanning electron microscopy, micro-probe X-Ray analysis, photoluminescence and photoconductance methods. Our investigations have shown that photoresponse of the CdS x Se 1-x films prepared by a screenprinting method can be suitable for the production of large-area photosensitive devices.

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Abstract.A comparative analysis of the characteristics of heat-conducting plastic was performed. The results of the thermal measurements of two of the same type 3W LED modules installed on heat sink with the same area of heat-dissipating surface made of aluminum and heat-conducting polymer have been presented. It has been shown that the overheating of LED module mounted on the heat-conducting polymer heat sink is 2…3 С higher than that on the aluminum heat sink (thermal conductivity is 20 times higher). The ranges of applicability of the heat-conducting plastics in LED technology have been determined.

We study experimentally the photoresistance of CdS-CdSe sintered granular films obtained by the screen printing method. We mostly focus on the dependences of photoresistance on film's microstructure, which varies with changing heat-treatment conditions. The minimum photoresistance is found for samples with compact packing of individual grains, which nevertheless are separated by gaps. Such a microstructure is typical for films heat-treated during an optimal time of 30 min at the temperature of 823 K. In order to understand whether the dominant mechanism of charge transfer is identical with the one in monocrystals, we perform temperature measurements of photoresistance. Corresponding curves have the same nonmonotonic shape as in CdSe monocrystals.Namely, photoresistance first increases with the growth of temperature, and then starts to decrease.Thus we conclude that the basic mechanism is also the same, as in monocrystals, and it is based on two types of centers in the forbidden gap. We suggest that the optimal heat-treatment time depends on two competing mechanisms: improvement of film's connectivity and its oxidation. Photoresistance is also measured in vacuum and in helium atmosphere, which suppress oxygen and water absorption/chemisorption at intergrain boundaries. We demonstrate that this suppression decreases photoresistance, especially at high temperatures.

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The thermal activation process of CdSe x S 1-x films, formed by screen printing, was investigated. We mostly focused on the influence of thermal treatment conditions on oxidised film formation on the crystalline grain surface with nano-barrier "dielectric-semiconductor" layer generation. The composition and thickness of nanobarrier layers were determined by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) methods. The thickness of nano-barrier layers was found to be 2-5 monolayers. It was shown that photoelectric properties of CdSe x S 1-x films were determined by the doping level and nano-barrier layer characteristics. By the use of XRD and SEM methods we experimentally investigated and justified that better microstructure and photoelectric properties (R D / R L ≥ 10 7) of CdSe x S 1-x films are achieved by photosensitivity activation during 15-30 min thermal treatment in quasi-closed air atmosphere at 550 °С or during 5-15 min at 600 °С with low speed cooling (3 °С/min). The manufacturing method for obtaining CdSe x S 1-x films with assigned characteristics determined by paste composition and properties, thermal treatment regime and medium optimisation was developed.

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