QC615 : Synthesis and characterization of chalcogenide nanostructured CuxS thin films and its alloys
Thesis > Central Library of Shahrood University > Physics > PhD > 2023
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Abstarct: In this thesis, the physical properties of thin films of CuxS nanostructures, of CFS ternary alloy compounds semiconductors thin films grown by spray pyrolysis method on glass substrates, and heterostructure Cu/CuS/p-Si/Al photodiodes are studied. In this research, the prepared samples were characterized by various methods, including Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-ray Spectroscopy (EDS), X-ray diffraction (XRD), UV-Vis spectroscopy, Hall effect, current-voltage (I-V) and current-time (I-t) measurements. CuxS thin films with different Cu/S molar ratios (Cu/S= 0.47, 0.45, 0.43 and 0.40) were grown at 285⁰C and then annealed at 200⁰C. The results showed that after annealing, the constituent grains of the laxyers are connected and the porosity of the films are increased. Also, it is found that the grown laxyers are mainly in the covellite CuS phase and after annealing the laxyers are composed of copper-rich secondary compounds and include the Cu2S (chalcocite) and Cu1.75S (anillite) phases. In the variation of thiourea molarity in the spray solution in the low concentration range (0.01, 0.015, and 0.02 M), it was found that with decreasing the thiourea concentration, the crystalline phase of chalcocite disappeared and the laxyers are turned into a single covellite phase. But, with increasing the amount of thiourea (0.02, 0.025, and 0.03 M), it was observed that the laxyers have a covellite phase (CuS) polycrystalline characteristics. By changing the spray solution's volume (10, 20, 35, and 50 mL), we found that the laxyers have a polycrystalline phase with a CuS hexagonal structure. Also, the Cu1.75S anillite phase was formed. Also, it is found that with increasing the volume, the electrical resistance of the laxyers are decreases. In the ternary CFS compounds we investigated the variations of molar ratios Fe/Cu= 0.2, 0.3, 0.4, 0.6 and then annealed at temperatures of 200 and 250⁰C. It is found that the samples have the CuFeS2 tetragonal chalcopyrite phase. Also, the secondary phase CuS covelite was observed. After annealing, it was observed that for the sample with a molar ratio of 0.6, the crystallinity is improved and the desired phase is observed in this sample. Also, for other samples, the crystallinity of the laxyers has increased after annealing. It was also found that with increasing the iron content, the electrical resistance of the samples is increased. Finally, the photodiode with Cu/CuS/p-Si/Al hetero-structure was fabricated with molar ratios of Cu/S= 0.40 and 0.45 and annealed at 200⁰C. The results showed that the as-grown and annealed samples have a covellite (CuS) phase. Also, it is found that compared to Si without a CuS laxyer, the optical reflectance (before and after annealing) is reduced, which indicates the increment in the absorption in the coated samples. The I-V results in dark conditions showed that the samples have rectification properties. Under light illumination in the visible range, it is found that while all the samples have a significant sensitivity to light radiation, the created photocurrent is higher in reverse bias conditions than in forward bias. The I-t data showed that the response and decay times of the samples are very small and around 16 ms.
Keywords:
#Thin Films #CuxS #CFS #Annealing #Spray Pyrolysis #Heterostructure Photodiodes. Keeping place: Central Library of Shahrood University
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