Microstructure and physical properties of nanostructured tin oxide thin films grown by means of pulsed laser deposition

Abstract The pulsed laser deposition (PLD) of tin oxide (SnO 2 ) thin films onto both alumina and quartz substrates have been achieved by ablating poly-SnO 2 pellets with a KrF excimer laser. At a laser fluence of ∼ 4.6 J/cm 2 , the effect of both background pressure (vacuum and 150 mTorr of oxygen) and deposition temperature ( T d ranging from 20 to 600 °C) were investigated. While all the films deposited under 150 mTorr of oxygen consisted of pure polycrystalline SnO 2 phase and were almost stoichiometric ([O]/[Sn] ∼1.9) even for T d as low as 20 °C, those deposited under vacuum were found to be composed of both amorphous SnO and poly-SnO 2 phases. Scanning and transmission electron microscopy observations have revealed that the micro-/nano-structure of the PLD SnO 2 films changes from a relatively porous fine-grained to a completely columnar microstructure as T d is raised from 20 to 600 °C. In particular, the average diameter of the SnO 2 nanograins was found to increase markedly (from 4 to ∼12 nm) when T d is increased from 20 to 450 °C and above. On the other hand, the resistivity (ρ) of the PLD SnO 2 films, deposited under 150 mTorr of oxygen, was found to decrease significantly from 200 to ∼2 Ω cm when T d is increased from 150 to 450 °C. The optical band gap ( E g ) of the PLD SnO 2 films increased from ∼2.6 to ∼4.0 eV when the deposition environment is changed from vacuum to 150 mTorr of oxygen while it is slightly affected by the variation of T d . The observed variations of ρ and E g are correlated to nanograin size variation and oxygen vacancies concentration in the films, respectively.