Structural properties of pure and Sn doped ZnO thin film prepared using sol-gel method

In this work, the pure ZnO and Sn doped ZnO thin films with different volume ratios (2, 4, 6, and 8V/V) of tin chloride have been successfully prepared by using sol-gel method. The structural properties were investigated by using X-ray diffraction (XRD), Scanning electron microscope (SEM), and Atomic force microscope (AFM). The results showed that, pure ZnO and Sn doped ZnO thin films have polycrystalline in nature with hexagonal structure. The structure have different plane at (1 1 1),(0 0 2),(1 0 1),(1 0 2),(1 1 0),(1 0 3),(1 1 2) belong to 2θ of 31.64, 34.30,36.13, 47.43, 56.49, 62.73, 67.83 respectively. The orientation of (002) at 2θ = 34.30 has a narrow FWHM, low strain, and crystalline size equal to 4.913, 3.683, 3.686, 2.455, and4.911 respectively for pure, Sn doped ZnO. Particle shapes were spherical granules morphology for all samples. The AFM images showed that the size of the grains on the surface of thin films increases with the increase in the concentration of impurity which agreement with the SEM results.


Introduction
Thin films of transparent conducting oxides (TCOs) have gained a lot of significance because of their possible applications in photovoltaic and optoelectronic devices. Among the TCOs, the ZnO compound that belongs to the (II-IV )group of semiconductor [1], which has a direct broad energy band gap of 3.37 eV and big excitation binding energy of 60 meV [2]. ZnO thin film has a great interest due to their typical properties ,such as abundant in nature, nontoxicity, thermal stability, high chemical [3]. ZnO thin films have a wide range of the applications including gas sensors, solar cells, laser systems, light emitting diodes (LED's), transparent electrodes, antibacterial activities [4][5][6][7][8][9], and so on. Furthermore, (ZnO) may be used in a variety of applications as a pure material such as display and optical devices or it may be doped with elements like (Al, Ag, or Sn) to be a high conductivity or elements of Magnet (Mn, Co, or Ni) as the diluted magnetic materials [10] . Moreover, zinc oxid may be prepared by a various techniques, such as chemical vapour deposition (CVD), magnetron sputtering, pulsed laser deposition (PLD), reactive evaporation, spray pyrolysis, piezoelectrical, solgel [11][12][13][14][15][16][17][18][19], and so on. The sol-gel method has some advantages in compare with other techniques because of excellent compositional control, and homogeneity level because of the lower 2 crystallization temperature and mixing of liquid precursor simultaneously, the sol-gel method shows the possibility to prepare a large and small area coating of the zinc oxide thin film with a low cost for technology applications [20]. In this work, the interest was focused on Sn doped ZnO thin films prepared by sol-gel spin coating method.

Experimental part
In order to prepare Pure and Sn doped ZnO thin film using sol-gel spin coating method, zinc acetate

structural characterization
The XRD pattern was achieved through the use of the(Cu K α ) radiation(λ= 1.54056 A˚) within the 2θ range from(20 o to 80 o ) ,and as an X-ray detector has been Panalytical PIXcel3D.The X-ray diffraction pattern evolution for pure and Sn doped ZnO thin film as showen in Figure( Figure(2-a). Moreover, Sn doped ZnO thin films have been reflected the some peaks as appearing in pure ZnO belong to Sn elements at 2θ=30.645,44.903,55.332,and 72.416 at plane(2 0 0), (2 1 1), (3 0 1),(4 2 0) respectively shown in Figure (2-b) ,which suggested that, the Sn doping has good linked with ZnO lattice; the other new peaks and shifted peaks to small distance due to fabrication of ZnSn(OH) which is become as result of ion exchange between the chlorides and HCl acid [21][22].

morphological characterization
Surface morphology of thin films is very important tool to investigate microstructure of thin films.
SEM micrograph of pure ZnO and doped Sn in a volume concentration (2,4,6 and 8)% thin films in Fig.2 (a-e) shows a homogeneous spherical granules spread over the surface of the film and it's similar size , and we note that the size of the granules increases with the increase in the concentration of impurity.       .

Conclusion
In this paper, pure ZnO and Sn doped ZnO in a various volume concentration (2,