Thin film heterostructures based on copper sulfide and tin dioxide for electronic applications

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Abstract
08-088 Luis Vicente de Andrade Scalvi Lima, J.V.(Universidade Estadual Paulista); Boratto, M.H.(Universidade Estadual Paulista); Scalvi, L.V.(Universidade Estadual Paulista); Tin dioxide (SnO2) have attracted a large number of researchers, due to applications as photothermal solar converters, gas sensors and optoelectronic devices. SnO2 thin films have become technologically important due to high reflectivity in the infrared and high transparency in the visible, along high electrical conductivity. 2% Eu3+-doped SnO2 thin films were obtained by sol-gel dip-coating and spin-coating, and annealed at 150°C, 250°C, 400°C and 500°C by 1h. Copper sulfide (Cu2S) was deposited between two layers of SnO2 forming the heterostructure SnO2/Cu2S/SnO2, and aluminum contacts were resistively evaporated on top of it. SnO2 is an n-type semiconductor even without doping. Eu3+ trivalent ions act as acceptors in the SnO2 matrix, leading to high charge compensation. Rare earth doped SnO2 shows applications in optoelectronics. CuxS is a p-type semiconductor, with direct bandgap ranging from 0.6 to 2.35 eV, depending on the structure. Transmittance data show that Cu2S decreases the heterostructure transparency compared to SnO2 over the entire spectra, yielding bandgap of 3.4 eV, close to the 3.6 eV of indirect transition in SnO2. Scanning electron microscopy confirmed the presence of SnO2 and Cu2S in the heterostructure. Confocal microscopy images allow verifying that heterostructures surfaces were homogeneous and with low roughness (18 to 38 nm). Cyclic voltammetry results yield a capacitive behavior for the analyzed heterostructures, which were confirmed by measurements and calculations of capacitance and hysteresis. Sample treated a 500oC shows 1µA for 1V of applied voltage, with capacitance of about 2x10-8 F and 0.77 of hysteresis. It was also verified that capacitance values does not show a direct relation with the calcination temperature. So far, it has been observed that the addition of Cu2S influences the optical and electrical properties of SnO2, leading to potential application as electrochemical capacitors (supercapacitors).
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