Structure, microstructure and photoluminescence properties of Fe doped SnO2 thin films
Introduction
Tin oxide (SnO2) is a well-known material for its applications in transparent conducting layers and gas sensors [1], [2]. However, pure SnO2 usually needs modifications in terms of additive incorporation to modify its conductivity, optical absorption and gas sensitivity. In particular, oxides of transition metals have been found to significantly influence the various properties of SnO2 thin films [3]. Among the various transition metal additives, Fe is of special interest because of its capability of grain growth inhibition within the SnO2 matrix [4]. Structure, optical absorption and gas sensing properties of Fe doped SnO2 thin films have been reported by a few groups and efforts have been made to establish structure–property relationships [4], [5], [6].
Different characterization techniques such as XPS, DLTS and luminescence spectroscopy can be employed to investigate the modified energy levels or defect levels in a material. Among these, photoluminescence (PL) investigations help in identifying various luminescent defect levels associated with a material and it serves as a technique to identify additional/modified defect levels generated by additive incorporation [7]. Additive materials, depending on their ionic radii and valence state, modify the crystal structure and defect chemistry of the host matrix. Hence interaction of the additives with the host material leads to either enhancement or quenching of PL peaks. Crystallite size also plays an important role in the positioning of the above PL emission lines. Hence qualitative estimation of grain size and signature of grain growth inhibition can also be performed by measuring peak shift in the PL spectrum.
PL investigations on tin oxide thin films and nanostructures have been reported in the literature [8], [9], [10], [11], [12], [13], [14]. However, the PL properties of Fe doped SnO2 thin films have not been studied so far. In the present work, the effect of Fe doping on crystalline structure, microstructure and PL properties of sol–gel derived SnO2 thin films are reported with an effort to identify the above discussed characteristics related to Fe doping.
Section snippets
Experimental
Thin films of SnO2 were deposited from a solution containing SnCl4.5H2O dissolved in an appropriate quantity of 2-propanol. Thorough mixing was ensured by refluxing the solution with a magnetic stirring arrangement for 24 h and the resultant solution was left ageing for another 24 h. This aged solution was then filtered to obtain a clear solution free of any particulates. Viscosity of the solution was controlled by mixing 50% volume of 2-methoxyethanol. To reduce crack formation during drying
Results and discussions
Fig. 1 shows the glancing angle x-ray diffraction patterns of SnO2 films for different Fe contents. The films are polycrystalline in nature with rutile structure having all peaks corresponding to the specific planes as shown in the figure. The relative intensity of all XRD peaks decreases in Fe doped films; it can be attributed to incorporation of Fe into the SnO2 lattice and the resultant decrease of crystallite size. It is also observed that the full width at half maxima (FWHM) ‘’ of the XRD
Conclusions
Fe doping leads to crystallite size reduction and higher strain in sol–gel spin coated SnO2 thin films. Contraction of unit cell volume and deformation of grain morphology with Fe doping are well supported by XRD analysis along with TEM and AFM micrographs. These changes in microstructure along with defect chemistry of Fe doping in SnO2 films lead to variation of the room temperature PL spectra compared to pure SnO2 films. Three principal PL peaks are observed which are shifted to higher
References (27)
Sens. Actuator B
(2005)- et al.
Thin solid Films
(2004) - et al.
Appl. Surf. Sci.
(2003) - et al.
Sens. Actuator B
(2006) - et al.
Sens. Actuator B
(2004) - et al.
Chem. Phys. Lett.
(2005) - et al.
Solid State Commun.
(2003) - et al.
J. Cryst. Growth
(2004) - et al.
Chem. Phys. Lett.
(2003) - et al.
Nanostruct. Mater.
(1997)