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Fabrication and Characterization of high photosensitivity CuS/porous silicon heterojunction photodetector

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Abstract

This study focused on the fabrication and characterization of CuS/porous Si heterojunction photodetector prepared by deposition of chemically sprayed CuS film on the porous silicon substrate prepared by anodization method. The optical and structural of CuS film and porous silicon PSi layer were investigated using x-ray diffraction, scanning electron microscope SEM, energy dispersive x-ray EDX, atomic force microscopy AFM, and UV-Vis optical absorption. XRD studies confirm the CuS film deposited on glass substrate was polycrystalline in nature with hexagonal structure, while the XRD data of the CuS film deposited on PSi shows only single peak at 2θ = 27° corresponds to (101) plane. The optical properties results reveal that the direct optical bandgap of CuS was around 2.25 eV. SEM shows that the average wall size and pore size of the porous silicon were 200 nm and 550 nm, respectively, and the CuS film consists of spherical grains with average grain size of 45 nm. AFM data illustrates that the root mean square of surface roughness of CuS film 9.1 nm. PL spectrum of PSi shows a strong emission peak at 576 nm. The optoelectronics properties of CuS/PSi/c-Si photodetector including dark and illuminated I-V characteristics, spectral responsivity, quantum efficiency, and detectivity were measured at room temperature. The responsivity of the photodetectors at peak of response 500 nm was 2.15 A/W.

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Novel sphere-like CuS hierarchical structures are fabricated by solvothermal approach without any surfactant and template. SEM and TEM characterizations show that the CuS sphere-like structures are composed of tens to hundreds of well-arranged and self-assembled nanoplates with a thickness of about 20 nm. The effects of dosage of CuCl2•6H2O, temperature and reaction time on the morphology of the products are systematically investigated and the results indicate that the CuS sphere-like hierarchical structures can only be obtained under certain experimental conditions. The possible formation mechanism of the CuS hierarchical structures is proposed. In addition, the possibility of using CuS as the electrode material for lithium ion batteries is studied.
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Thin films of CuxS are deposited by both chemical vapor deposition (CVD) and atomic layer deposition (ALD) using copper bis-tetramethylheptanedionate, Cu(thd)2, and H2S as the precursors. Single-phase CuS and Cu1.8S can be deposited using both techniques, while in CVD also mixed phases can be formed. Comparing the ALD process with the CVD process leads to a better understanding of the reaction chemistry of both processes. The main factor is the decomposition of Cu(thd)2 at 175 °C, which leads to a phase transition from CuS to Cu1.8S in ALD and deposition of mixed phases in CVD. Consequently, the phase transition is sharp in ALD and gradual in CVD. At temperatures higher than 250 °C, decomposition of Cu(thd)2 occurs in the gas phase, leading to a transition from a reaction-limited regime to a thermodynamic regime in CVD and to loss of uniformity and homogeneity in ALD.
Article
The growth of copper sulfide thin films by the successive ionic layer adsorption and reaction (SILAR) method at room temperature and normal pressure was studied. The CuS films were characterized by chemical analysis, XRD, SEM and UV spectroscopy. The growth rate of CuS was proportional to copper precursor concentration. The films were polycrystalline and showed no preferred orientation. The surface of the CuS thin films was rough compared with CdS films, which were used as buffer layer on ITO and glass substrates to enhance the weak adhesion of CuS to oxide surfaces.
Article
High-performance rectifying contacts with a rectifying ratio exceeding 1000 are obtained by depositing thin transparent and conducting CdO films on porous silicon (PSi) and annealing at an optimized temperature. The reverse current of 1.5 mm diameter diodes at -10 V in the dark is 26 nA this increases by three orders of magnitude under exposure to normal tungsten lamp illumination. The results show that CdO-on-PSi diodes will act as very good candidates for making high-efficiency photodiodes.
Article
Four kinds of copper sulfides of different chemical compositions were chemically deposited and examined for their optical and electrical characteristics. Electroless chemical deposition from aqueous copper thiosulfate baths in acidic media was used to deposit thin films of Cn2S, Cu1.8S, Cu1.4S, and CuS on glass, polyester, or metal substrates. Rutherford back scattering analysis was used to determine the chemical composition of the films. The optical characteristics of the films were studied in the UV-VIS-NIR region, between 0.3 and 2.5 μm. Cu2S films were found to be highly transmissive throughout the spectral region 0.5-2.5 μm. The transmission in the near-infrared region (0.8-2.5 μm) decreased as the chemical composition approached the stoichiometry of CuS, which was found to be highly absorptive for the near-infrared radiation. All films displayed high electrical conductivity, with the CuS film being the most conductive and conductivity decreasing toward the copper-rich phase, Cu2S. All films were found to be p-type semiconductors. The optical energy band gaps of the films were also studied and it is shown that the values can differ, depending on the method of determination. Some practical applications of these films are also discussed.
Article
We present the rational synthesis of colloidal copper(I) sulfide nanocrystals and demonstrate their application as an active light absorbing component in combination with CdS nanorods to make a solution-processed solar cell with 1.6% power conversion efficiency on both conventional glass substrates and flexible plastic substrates with stability over a 4 month testing period.