Abstract
Post-deposition annealing by ultra-short laser pulses can modify the optical properties of SnO₂ thin films by means of thermal processing. Industrial grade SnO₂ films exhibited improved optical properties after picosecond laser irradiation, at the expense of a slightly increased sheet resistance [Proc. SPIE 8826, 88260I (2013)]. The figure of merit ϕ = T¹⁰ / R(sh) was increased up to 59% after laser processing. In this paper we study and discuss the causes of this improvement at the atomic scale, which explain the observed decrease of conductivity as well as the observed changes in the refractive index n and extinction coefficient k. It was concluded that the absorbed laser energy affected the optoelectronic properties preferentially in the top 100-200 nm region of the films by several mechanisms, including the modification of the stoichiometry, a slight desorption of dopant atoms (F), adsorption of hydrogen atoms from the atmosphere and the introduction of laser-induced defects, which affect the strain of the film.
Highlights
Tin-dioxide (i.e. SnO2), known as stannic oxide, is a widely applied and studied ceramic material [2]
By careful selection of the laser parameters, heat accumulation can be controlled in order to increase the duration of the heating cycle time, while ensuring that the temperature at the film/substrate interface remains below the damage threshold for the substrate
As already discussed in our previous work [1], the nano-structures observed in Fig. 1(c) and Figs. 2(e)-2(f) on the SnO2 film treated at high laser fluence are Laser-induced Periodic Surface Structures (LIPSSs)
Summary
Tin-dioxide (i.e. SnO2), known as stannic oxide, is a widely applied and studied ceramic material [2]. Laser annealing is an alternative use of ultra-short pulsed laser sources, as a future prospect, in thermal processing, e.g.: extremely selective annealing, laser selective evaporation (either for removal of unwanted impurities or for tailoring the stoichiometry), ‘ultra-selective’ laser doping, etc. The present research aims to study the effect of UV (λ = 343 nm) picosecond lasermaterial interaction on the microscopic structure of SnO2 thin films in order to explain the origin of the macroscopic changes observed in the optical, as well as electrical properties of the film. The possible causes, which induce a modification of the carrier density, electronic mobility and optical constants n and k, due to the laser treatment, were examined by means of several inspection techniques The results of these analyses were cross-checked to give an overall exhaustive comprehensive interpretation of the observed effects. The results of this study can be used to further improve the performance of SnO2-based electrodes for solar cells and/or other electronic devices
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