Microscopic and chemical analysis of room temperature UV laser annealing of solution-based zinc-tin-oxide thin films

Abstract

As a promising transparent semiconducting oxide (TSO) candidate, zinc-tin-oxide (ZTO) thin films were fabricated by combining solution coating and ultraviolet (UV) laser annealing. Instead of external heating, an intense UV laser was applied to transform sol-gel coatings via surface heating and photoexcited dissociation into oxide films. The laser-induced phase transformation was extensively investigated with synchrotron-based X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and electron energy loss spectroscopy (EELS). The chemical states and microscopic distributions of oxygen, zinc, and tin were significantly modified during the laser irradiation. Relative oxidation and surface migration between zinc and tin gradually evolved toward a combination of ZnO1−x host and SnO2−y grains. Our results present deeper insight into the use of UV laser annealing for developing a room temperature (RT) fabrication method of TSO thin films and other relevant solution coatings.

Application of Laser Treatment in MOS-TFT Active Layer Prepared by Solution Method

“…Therefore, in order to prepare high quality thin films, the removal of impurities is crucial. In order to prepare high quality metal oxide thin films, it is necessary not only to remove the impurities contained in the precursors, but also to provide enough energy to promote the Polycondensation and the densification of the thin films to form the metal-oxygen-metal (M-O-M) lattice structure [52][53][54][55]. The improvement of the lattice structure and the densification of the thin film help to reduce the traps and the potential barrier, increase the carrier mobility, and then improve the device performance of MOS-TFT [43,47,53,54,[56][57][58][59][60].…”

“…Laser treatment can effectively remove the impurities in the precursor film and promote the formation of lattice network [29,54,55,[61][62][63][64][65]. There are usually three mechanisms for the interaction between laser and precursor film: (1) thermal effect of laser; (2) photochemical cleavage of metastable bonds; and (3) photochemical effect.…”

“…The process of thermal effect of laser usually includes: (1) carrier excitation; (2) carrier-carrier scattering, carrier-phonon scattering, and energy transfer to the lattice due to spontaneous phonon emission; (3) when the carrier and lattice reach equilibrium, the film is heated, as shown in Figure 4 [51,66]. High energy photons can induce the photochemical cleavage of chemical bonds related to metal alkoxy and carbon impurities and promote the subsequent reorganization of metal oxide frames [27,55,63]. These mechanisms are also observed in other light-assisted methods.…”

“…Therefore, in the process of laser treatment, temperature gradients are easy to exist in the film, resulting in differences in the properties of regions with different depths of the film. This effect is particularly significant in the films treated by ultraviolet wavelength lasers [55,98,99]. Kwon et al prepared ZTO thin films by sol-gel method and treated them with KrF excimer laser.…”

“…regions with different depths of the film. This effect is particularly significant in the film treated by ultraviolet wavelength lasers [55,98,99]. Kwon et al prepared ZTO thin film by sol-gel method and treated them with KrF excimer laser.…”