Photoconductivity of CdS-CdSe granular films: influence of microstructure

We study experimentally the photoconductivity of CdS-CdSe sintered granular films obtained by the screen printing method. We mostly focus on the dependences of photoconductivity on film's microstructure, which varies with changing heat-treatment conditions. The maximum photoconductivity 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 intermediate (optimal) time. 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 peculiar nonmonotonic shape as in CdSe monocrystals, from which we conclude that the basic mechanism is also the same. It is suggested that the optimal heat-treatment time appears as a result of a competition between two 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 increases photoconductivity, especially at high temperatures.Comment: 12 pages, 8 figures, final versio

Physicochemichal Features of Dielectrical Nano-Barrirer Layers in CdSexS1-x Films Formed by Screen Printing Method

The thermal activation process of CdSexS1-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 nano-barrier 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 CdSexS1-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 (RD / RL ≥ 107) of CdSexS1-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 CdSexS1-x films with assigned characteristics determined by paste composition and properties, thermal treatment regime and medium optimisation was developed

Physicochemichal Features of Dielectrical Nano-Barrirer Layers in CdSexS1-x Films Formed by Screen Printing Method

The thermal activation process of CdSexS1-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 nano-barrier 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 CdSexS1-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 (RD / RL ≥ 107) of CdSexS1-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 CdSexS1-x films with assigned characteristics determined by paste composition and properties, thermal treatment regime and medium optimisation was developed