Browsing by Author "Jayadevan, KP"

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Dielectric characteristics of nanocrystalline Ag-Ba0.5Sr0.5TiO3 composite thin films
(2004-08-16)
Jayadevan, KP
;
Liu, CY
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Nanocrystalline Ag-Ba0.5Sr0.5TiO3 (Ag-BST) composite thin films are deposited on Pt/Ti/SiO2/Si substrates by a sol-gel method. The voltage-dependent capacitance (C-V) and dielectric loss of the films decrease with increasing Ag up to 2 mol % due to a series configuration involving low dielectric interface layers and dense microstructures. The evidence for asymmetric distribution of charge carriers in the Ag-BST film is derived from C-V measurements. The dielectric tunability of BST film with 1 mol % Ag is comparable to that of pure BST. (C) 2004 American Institute of Physics.
One-dimensional semiconductor nanostructures as absorber layers in solar cells
(2005-11-01)
Jayadevan, KP
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The one-dimensional (1-D) nanostructures of cadmium chalcogenicles (II-VI: CdSe, CdTe), InP and GaAs (III-V), and the ternary chalcopyrites CuInS2, CuInSe2, and CuInTe2 (I-III-VI2) are the candidate semiconductors of interest as absorber layers in solar cells. In the confinement regime (similar to 1-10 nm) of these 1-D nanostructures, the electronic energy levels are quantized so that the oscillator strength and the resultant absorption of solar energy are enhanced. Moreover, the discrete energy levels effectively separate the electrons and holes at the two electrodes or at the interfaces with a polymer in a hybrid structure, so that an oriented and 1-D nanostructured absorber layer is expected to improve the conversion efficiency of solar cells. The intrinsic anisotropy of II-VI and I-III-VI2 crystal lattices and the progress in various growth processes are assessed to derive suitable morphological features of these 1-D semiconductor nanostructures. The present status of research in nanorod-based solar cells is reviewed and possible routes are identified to improve the performance of nanorod-based solar cells. Finally, the characteristics of nanorod-based solar cells are compared with the dye-sensitized and organic solar cells.
Surface chemical and leakage current density characteristics of nanocrystalline Ag-Ba0.5Sr0.5TiO3 thin films
(2005-09-01)
Jayadevan, KP
;
Liu, CY
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Nanocrystatfine chi Ag-(1-x)Ba0.5Sr0.5TiO3(Ag-BST, 0 <= x <= 0.1, where x is the mole fraction of Ag) thin films have been deposited on Pt/Ti/SiO2/Si substrates by a sol-gel method. The films have been characterized by X-ray diffraction (XRD), scanning electron microscopy, and X-ray photoelectron spectroscopy (XPS). The core-level XPS of oxygen (O1s) of the Ag-BST films indicate that an optimum amount of Ag (x = 0.02 or 2 mol%) enhances the binding energy of oxygen, possibly through a mechanism in which the electrophilic oxygen dissociates from the Ag surface and fills the oxygen vacancies. Similarly, the binding energy of Ag (Ag3d) shows a shift toward a higher value with increasing Ag up to 4 mol%, probably because of the chemical shift of Ag in BST along the surface layers, surface relaxation, or changes in the Fermi level of small Ag particles in the solid solution range of Ag in BST fillms (x <= 0.04). The leakage current density of 2 mol% Ag-added BST (similar to 10(-6) A/cm(2)) is less by about an order of magnitude than pure BST at an electric field of 200 kV/cm. A defect model is proposed to explain the observed leakage current density of Ag-BST films satisfactorily.