Analysis of Sn Concentration Effect on Morphological, Optical, Electrical and Photonic Properties of Spray-Coated Sn-Doped CdO Thin Films
Tin-doped cadmium oxide (Sn:CdO) transparent thin films with different Sn concentrations were deposited on glass and p-silicon substrates by the chemical spray method at 250 • C. Different concentrations of stannic chloride were used to prepare Sn:CdO thin films. The prepared doped and un-doped CdO films were subjected to X-ray diffraction (XRD), scanning electron microscopy and atomic force microscopy, optical absorption, and electrical analyses to characterize their structural, morphological,
... optical, and electrical properties, respectively. XRD analysis demonstrated the growth of polycrystalline and cubic CdO with preferential orientation along the (111) plane. Sn-doping shifted the XRD peaks slightly towards a higher Bragg angle and increased the band gap of CdO thin films. Variation in doping concentration also affected the morphology of the films. Optimum Sn-doping increased the electrical conductivity of CdO thin films. Furthermore, to the best of our knowledge, the photoresponse analyses of the fabricated un-doped and doped n-CdO/p-Si heterostructures were performed for the first time in this study. For the growth of CdO and Sn-doped CdO (Sn:CdO), a variety of techniques such as pulsed laser deposition [13,19], metal-organic chemical vapor deposition (MOCVD) , successive ionic layer adsorption and reaction (SILAR) , chemical bath deposition , RF magnetron sputtering , sol-gel processing , thermal evaporation , and spray pyrolysis  are used. Amongst all, the spray pyrolysis method is quite enticing due to its simplicity, ease of composition control, and better doping possibilities. In this study, we aim to investigate the effects of Sn-concentration on morphological, structural, optical, and electrical properties of Sn:CdO. Sn-doping-induced better optical and electrical properties improve the overall performance of TCO-based solar cells and other optical devices. However, Sn:CdO growth by a variety of methods is already explained by several research groups [18, 22, 24] ; however, information on spray-coated Sn:CdO growth is limited. Moreover, to the best of our knowledge, the n-Sn:CdO/p-Si heterostructure and photoresponse analyses are propounded for the first time. Generally, Sn:CdO is used for window layers in photovoltaic applications because of its high transparency in the visible region. However, as a high band gap n-type semiconductor, Sn:CdO-based heterojunction solar cells can also be fabricated on p-Si substrates. In addition, the heterojunction formed between Sn:CdO and p-Si can minimize recombination loss due to a combination of high band gap window material and small band gap absorber material. Hence, besides probing into the material properties, this study is focused on testing the photoresponse mechanism of n-Sn:CdO/p-Si heterojunction diodes.