Optimization of indium oxide thin films properties prepared by sol gel spin coating process for optoelectronic applications

Abstract

Indium oxide thin films have been deposited by sol-gel spin coating technique using indium (III) nitrate hydrate, absolute ethanol and acetylacetone as precursor solution, solvent and stabilizer, respectively. The effect of the molar concentration, annealing temperature, titanium doping and cupric doping on the structural, morphological, optical and electrical properties of In2O3 films have been studied. All films have been characterized by multiple techniques such as X-ray diffraction (XRD), UV-Visible spectroscopy, scanning electron microscope (SEM), photoluminescence (PL) spectroscopy, Fourier transform infrared (FTIR) spectroscopy and four probe method to investigate the physical properties of indium oxide films. X-ray diffraction analysis showed that the films are polycrystalline in nature having cubic crystal structure with preferred growth orientation along (222) plane. SEM images show that the films are homogenous, uniform and dense without any pin holes and cracks. The transmittance of In2O3 films was high up to 90% and it is probably related to the good crystalline quality of the films. The optical gap was found to vary between 3.5 and 4.0 eV. The photoluminescence measurements revealed mainly three emission peaks (ultraviolet, blue and green) corresponding to the near band edge (NBE) and defect levels (DL) emissions. The broad ultraviolet luminescence peak 310-420 nm is assigned to NBE emission. The blue and green luminescence are attributed to DL emission. The electrical measurements revealed that prepared Cu doped In2O3 films have a low resistivity (about 1.77×10-3 – 6.34×10-3 (Ω.cm)) which made these films suitable for optoelectronic applications.