Abstract
Pd-F:SnO2 thin films have been prepared by spray pyrolysis technique. Optimization has been done by doping SnO2 with palladium at varying levels of concentration and then recording sheet resistance. The sheet resistivity has been observed to decrease gradually as at% Pd concentration is increased; an optimum sheet resistivity value of 2.71 × 10−2 Ω cm has been recorded. The decrease in sheet resistivity has been attributed to presence of Pd ions which contribute in increment of charge carrier density. Using the optimum value of at% Pd doping, the same procedure has been repeated to study the effect of fluorine on Pd:SnO2; an optimum value of 1.64 × 10−4 Ω cm sheet resistivity has been recorded. This decrease has been attributed to substitution of O− with those of fluorine hence improving charge carrier density. The effect of passivation has been studied by comparing as prepared, annealed and passivated Pd-F:SnO2 thin films. Annealing has been observed to decrease the sheet resistivity to 1.21 × 10−4 Ω cm, while passivation has the effect of increasing the sheet resistivity to 1.53 × 10−4 Ω cm which is attributed to effects resulting from annealing the samples in nitrogen gas atmosphere.
Highlights
The SnO2 based thin films have received a great deal of interest from many researchers due to their numerous applications which include window layer for solar cells, gas sensors, opacities, thin film resistors, electric conversion thin films, surface protection layers of glass, semiconductor hetero-junction structures, heat reflective semiconductor insulators, an overcoat for thin film magnetic media over-coat and as a material for Li-ion batteries [1]
Undoped SnO2 thin films had a low sheet resistivity of 5.992 × 10−1 Ω cm which can be attributed to deviation from stoichiometry due to creation of oxygen vacancies which act like electron donors and increase free carrier concentration [11,24]
On doping the SnO2 with palladium, the sheet resistivity of Pd:SnO2 has been observed to decrease due to the presence of Pd ions into the crystal lattice which contributes more electron ions into the lattice increasing electron carriers
Summary
The SnO2 based thin films have received a great deal of interest from many researchers due to their numerous applications which include window layer for solar cells, gas sensors, opacities, thin film resistors, electric conversion thin films, surface protection layers of glass, semiconductor hetero-junction structures, heat reflective semiconductor insulators, an overcoat for thin film magnetic media over-coat and as a material for Li-ion batteries [1]. In this study SnO2 based thin films were prepared for gas sensing applications. SnO2 based thin films are polycrystalline with tetragonal rutile structure, non-stoichiometric, degenerate n-type semiconductor [2,3,4]. SnO2 based thin films do not react with oxygen and water vapor and can only be attacked by hot alkalis [7]. Electrical conductivity of SnO2 thin films can be improved by codoping SnO2 thin films with Pd and F [8,9,10]
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