Synthesis and characterization of tin oxide and copper doped tin oxide thin films by spray pyrolysis

Abstract

Tramparent conducting tin OXldc(SOOl) thin films are of great interest due to their vanety of applications in devices as wmdow layers, heat reflectors in solar cells, LIght em;ttmg diodes (LEDS), hquid crystal dl"plays, various gas sensors etc. Pure Sn02 and copper doped S002 thin films have been deposited onto glass substrate by spray pyrolysis method. Oeposition parameters: substrate temper<!ture, deposition time and flow rate of solution, amount of base material, distance between the substrate and spray gun tip was kept constant Tiil chloride and copper mlrate were used a5 source of lin (Sn) and copper (Cu). The doping concentration of eu ",as varied from 1-8 wt, %. The surfuce morphological, structural, electrical and optIcal propertlCS of the as-deposited tin oXIde f,lms have been investigated as a function ofeu-doping level, The as-deposited films are found homogeneous. The thiclmess of the films was estimated by Fizeau fringes interference method, The films thicknesses "fere varied from 190 to 210 nm, The scanning electron mlCroSCOpy(SEM) micrographs of as-deposited film show unifonn surface and dep<Jsitioncovers the substrate well. Energy Dispersive Analys's of X-ray (EDAX) results clearly showed that the grains were typically compnsed of both Sn and 0 for pure and Sn, oxygen (0) and Cll for eu doped films. From EDAX (EDX) data it was found that atomic weight % of ell is increased with thc increase of Cu concentration in Cu doped SnO, fihns. X-ray dlfTraction stlldies show the polycrystalline natllre of the films with prererentlal orientation along the (110), (i01), (200), (210), and (211) planes and an average gram size of 7.244579 A. The peaks were found to shift from their standard positions in the presence oftlle Cu dopan/. There is a, dev'at,on in the lattice pammetcrs and it may be happened due to the pO~ltioningof dopant atoms into the interstitiallauice sites. The transmittance and absorbance spectra for the as-deposited films were recorded ill the wavelength range of 190 to 1100 nrn. The optical transmission of the films was found to inerease from 71 % to 79 % (at millal) WIth thc addihon of Cu up to 4% and then decreases for higher percentage of copper doping Optical constants such as band gap and refractive index were calculated from the ultra-violet transmittance and absorption graphs. IV The optical band gap for pure 1m oxide film is found to be 3.75 ev' Due to eu dopmg, the band gap is shifted to lower energies and then increases further wlth inereasmg concenlratJOIl of the dopants, The refractiv-e index of the films is found 1,63 and the 'lallatIon of refractive index is observed due to Cn concentrations and the lowest value of refr;active mdex ISfound to be 1.54 for 4% eu doped SnO:>thm films, The high eleL1riC'llconduct;vity has been found for 4 wI. % CuNO, +% wt % S1l02. The films deposlled al optimized deposltions show electrical resistivity, p 5.1065~ IO-'n-m, conductiVIty, (I =1.9582~l03 (n-mr' and sheet resistance of 2.5532 xlO' f)/o at room temperature 305 K obtained for 200 nm thick SnO:>thin film. The reslStiVlty of SnO) films is fOlmd to decrease from 4,5095~10-' Hm to Ll395~ 10-4 nm as the Cu doping is varied [rom 1% to 4%, and above 4% eu doping II IS again increased. ActIvation energy of the samples varies from 0.022896 to 0.058889 eV. It is evident from the prescnt study that the Cn doping promoted the film morphology and also its structural, optical and electrical properties of the films