Tuning of optical bandgap, conductivity parameters, and PL emissions of SnO2:Ni thin films under Ar, N2, and O2 annealing

The influence of annealing atmosphere (N-2, Ar, and O-2) on optical properties and electrical parameters of SnO2:Ni thin films prepared by sol-gel process was investigated. The XRD results showed that the samples possessed tetragonal rutile-type phase, as well as Ni-doped SnO2 thin film under N-2 annealing ambience revealed no distinct peaks. The FESEM images revealed that the film surface is constituted by homogenous spherical nanograins. The transmittance spectra of the films showed that O-2 annealing enhanced the transparency of the films. The optical measurements yielded that annealing under oxygen led to the lowest extinction coefficient while annealing in Ar caused to the highest refractive index of SnO2:Ni thin films. The film annealed in O-2 has the highest band-gap value, whereas Ar annealing reduced the band-gap value. The PL spectra disclosed an intense blue emission in N-2 ambience. The Hall effect measurements indicated that the best electrical response (conductivity, carrier concentration, and mobility) in prepared samples is reached after annealing in Ar ambience. In addition, annealing in the O-2 atmosphere converted the conductivity type of Ni-doped SnO2 thin films from n-type to p-type.