Optical, structural, morphological, and compositional properties of cobalt doped tin oxide (CTO) thin films deposited by modified chemical bath method in alkaline medium

Abstract

Tin oxide and cobalt doped tin oxide (CTO) thin films were successfully deposited using modified chemical bath method with tin (II) chloride dihydrate and cobalt chloride hexahydrate as precursors for Sn and Co ions respectively, in the presence of ammonium hydroxide as source of oxygen and pH adjuster. The samples obtained were annealed for 4 h at a temperature of 673 K and characterized for optical, structural, morphological and compositional analysis. The films exhibit low absorbance values (0.02–0.31) and low reflectance values (2.14%–20.10%) which varies directly with cobalt ion (Co2+) concentration. The transmittance values (48.64%–96.16%) of the films are high and varies inversely with cobalt ion (Co2+) concentration. The refractive index varies directly with increasing cobalt ion concentration and ranges from 2.60 to 1.49 for doped film and 1.34 for the undoped SnO2. Extinction coefficient of the films varies directly with cobalt ion concentration. The films have wide band gap, (2.90 eV–2.72 eV for doped films and 3.05 eV for undoped SnO2 thin film). Structural analysis revealed that the films are of tetragonal rutile phase of SnO2 with mineral name of cassiterite and confirmed that the grain sizes of the deposited films range from 10.99 nm to 9.40 nm. The dislocation density ranged between 8.28×10−3(line/nm2) and 11.32×10−3(line/nm2) while the microstrain obtained ranged between 6.07×10−3 to 12.03×10−3. The compositional results revealed the presence of the Sn, Co, O2 and some traces of other elements. The SEM images obtained show uniform surface without any voids or flaws. The micrographs show that the surfaces are composed of particles of slightly different sizes.