Effect of indium doping on the UV photoluminescence emission, structural, electrical and optical properties of spin-coating deposited SnO2 thin films

Abstract

Undoped SnO2 and indium doped SnO2thin films, with different indium concentrations (1, 2, 3 and 4at.%), synthesized by sol-gel spin-coating method on glass substrates were investigated using X-ray diffractometer (XRD), atomic force microscopy (AFM), UV–vis spectroscopy, photoluminescence spectroscopy (PL) and four-point probe measurements. The XRD patterns showed that all of the films are polycrystalline with tetragonal rutile structure and the crystallite sizes are found to decrease with indium doping from 7.58 nm to 6.62 nm. The AFM results of our films indicated that the surface roughness decreases with indium doping. All the samples have a high transmittance, greater than 80 %, in the visible range with an optical band gap varying from 3.82 eV to 3.75 eV. The room temperature photoluminescence spectra showed the same position of peaks for each emission. The peak at 324.4 nm corresponds to the excitation transitions from the conduction band to the valence band, the other emission peaks are related to oxygen vacancies (VO°, VO+, VO++) which are centred at 364, 379, 418, and 467 nm. Furthermore, the decreased intensity of the PL curves was linked to the diminution in oxygen vacancies during indium doping. The strong and narrower UV light emission peak was observed for sample doped with indium 1at.% which can be applicable for ultraviolet light emitting diodes (UV-LEDS).These films displayed low electrical resistivity ranging between 2.25 × 10−3 and 4.95 × 10−3 Ω cm.