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Sheo K. Mishra,Rajneesh K. Srivastava,S.G. Prakash,Raghvendra S. Yadav,A.C. Panday 대한금속·재료학회 2011 ELECTRONIC MATERIALS LETTERS Vol.7 No.1
In this paper, cadmium sulfide (CdS) quantum dots (QDs) are synthesized by a simple co-precipitation method. X-ray diffraction (XRD) confirmed the formation of a cubical zinc blend structure of CdS nanoparticles. Transmission Electron Microscopy (TEM) images revealed that the CdS QDs are of 2-5 nm in size. The UV-vis absorption spectra showed an absorption peak at 427 nm (~2.90 eV) indicating a blue shift of 0.48eV as compared to bulk CdS. We estimated the particle sizes with the help of X-ray diffraction (XRD) patterns (3.665 nm) and the shift of the band gap absorption in the UV-vis spectrum (4.276 nm), which is very close to the TEM micrograph result. The photoluminescence spectrum shows three major emission peaks centered at 453 nm (~2.73 eV), 526 nm (~2.35 eV) and 551 nm (~2.24 eV) at room temperature, which may be attributed to excitonic transitions, donor-acceptor (D-A) pairs recombination and the sulphur interstitial defects (Is) present in the band gap. To study the photoconductivity, the field dependence of the photocurrent and the dark-current was assessed, as was the time-resolved rise and decay photocurrent spectrum and wavelengthdependence photocurrent spectrum assessment of the CdS QDs. The time-resolved rise and decay photocurrent spectra exhibited negative photoconductivity (NPC) behavior when the CdS QDs were illuminated with 490nm light. Such anomalous NPC may be attributed to the light-induced desorption of water molecules. The wavelength-dependence of the photocurrent was found to be close to the absorption and PL spectrum. The photoconductivity properties of the CdS QDs were measured using a thick film of powder without any binder. These CdS QDs can find potential application in optoelectronic devices and photodetectors.
Effect of Indium Doping and Annealing on Photoconducting Property of Wurtzite Type CdS
Vineet Kumar Singh,Pratima Chauhan,Sheo Kumar Mishra,Rajneesh K Srivastava 대한금속·재료학회 2012 ELECTRONIC MATERIALS LETTERS Vol.8 No.3
In this paper we observed the effect of doping and annealing on the dark current and anomalous photoconducting behavior of hexagonal wurtzite CdS, synthesized by solid state reaction method. Undoped CdS sample shows higher anomalous behavior in photoconductivity as well as contains larger dark current of 19 nA. With the doping of Indium in CdS, dark current decreases from 19 nA to 1 nA but the anomalous behavior is not completely removed. While, after annealing at 150°C for four hour, indium doped CdS sample shows good switching property with rise and decay time of 360 ± 10 & 322 ± 6 seconds respectively. The anomalous photoconducting behavior is completely removed from annealed sample. X-ray diffraction patterns confirm the existence of hexagonal wurtzite phase of indium doped and undoped CdS samples while energy dispersion X-ray spectrum exhibits the elemental presence of cadmium, indium & sulfur in the indium doped sample. UV-Visible absorption spectra show the blue shift in absorption edge on indium doping from 475 nm to 425 nm in comparison to undoped sample. Photoluminescence spectra confirm the indium doping and reveal that annealed CdS sample has lesser defects among other samples due to which annealed sample has best switching performance.