Abstract
Zinc oxy-selenide Zn(O,Se) is a novel material, that can replace the toxic CdS buffer layer in thin film solar cells and other optoelectronic devices. In this paper a systematic study of the structural, optical and electrical properties of Zn(O,Se) layers, grown by pulsed laser deposition under 50 mTorr of nitrogen background pressure, over a wide range of the substrate temperature, from RT to 600 °C, is reported. XRD, Raman, HR-SEM, XPS, UV-Vis techniques and Hall effect measurements have been used to investigate the structural, and optoelectronic properties of Zn(O,Se) layers. XRD analysis revealed that the polycrystalline ternary Zn(O,Se) phase formed at 500 °C. Raman analysis confirmed the formation of the polycrystalline Zn(O,Se) phase at 500 °C and an amorphous phase at substrate temperatures below 500 °C. Similarly, XPS analysis accompanied with the modified Auger parameters confirmed formation of ternary Zn(O,Se) layer at 500 °C as well. HR-SEM investigation showed the growth of homogenous, dense and adherent films onto a glass substrate. Furthermore, optical studies revealed that all prepared films are practically transparent in the visible region of the spectrum, with a band gap around 3 eV. Hall effect measurements revealed that conductivity, and electron concentration, increased by four orders of magnitude at 600 °C. It was found, that nitrogen background pressure maintained stable ratios of elemental contents in the whole range of the substrate temperature for Zn(O,Se) layers.
Highlights
An urgent global need for sustainable energy resources has opened a multi-disciplinary research area towards potential clean energy resources, such as solar cells and hydrogen generation[1], as renewable energy sources
According to X-ray diffraction (XRD) results all Zn(O,Se) layers deposited below 500 °C were amorphous
The diffraction peak located at approximately 30.94° has been shown, in the literature, as corresponding to (002) plane ZnO1-xSex in which the x values varied from 0 to 0.121
Summary
An urgent global need for sustainable energy resources has opened a multi-disciplinary research area towards potential clean energy resources, such as solar cells and hydrogen generation[1], as renewable energy sources. It was demonstrated that during the cell processing, CdSe diffused into CdTe, converting itself from photo-inactive CdSe to photo-active, low band gap, CdTe1-xSex[23,24] with the successful removal of the undesired CdSe sub-layer In other words, this approach extended photon collection to a longer wavelength, reduced losses in short wavelength and increased the carrier lifetime so giving excellent device performance[22,25]. The aim of this work was the deposition of Zn(O,Se) thin films by PLD under nitrogen back-pressure and different substrate temperatures (Ts), with the study of the structural and optoelectronic properties of the prepared Zn(O,Se) layers. Special attention was paid to the comparison between Zn(O,Se) layers deposited in high vacuum and under nitrogen back-pressure
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