Electrical, optical and structural properties of Li-doped SnO_2 transparent conducting films deposited by the spray pyrolysis technique: a carrier-type conversion study

摘要

In this paper, we investigate the electrical, optical and structural properties of Li-doped SnO_2 transparent conducting films deposited on glass substrates by the spray pyrolysis technique. The SnO_2:Li thin films were deposited at a substrate temperature of 480℃ using an aqueous ethanol solution consisting of tin and lithium chloride with various doping levels from 0 to 25 wt% in solution. The effect of increasing Li concentration on the electrical, optical and structural properties of SnO_2 films has been studied. The results of x-ray diffraction have shown that the deposited films are polycrystalline without any second phases with preferential orientations along the (110) and (211) planes and an average grain size of 28.7 nm. Also, the Hall effect and resistivity measurements of the films show that for a specific acceptor dopant concentration of ～2 wt% or [Li]/[Sn] atomic ratio equal to 37 at% in solution, the majority of carriers convert from electrons to holes and for a Li concentration of ～15 wt% in solution, p-conductivity increases sharply. The optical absorption edge for undoped SnO_2 films lies at 4.11 eV, whereas for high acceptor doped films it shifts towards lower energies (longer wavelengths) in the range of 4.11 to 3.61 eV.