Modifications in structure, surface morphology, optical and electrical properties of ZnO thin films with low boron doping

Boron doped zinc oxide (ZnO:B) thin films with low B concentration, varied between 0.50 and 1.50 atomic percentages (at%) are prepared at substrate temperatures (T-S) between 300 and 450 degrees C using spray pyrolysis technique. Polycrystalline wurtzite structure is observed in the X-ray diffraction patterns of ZnO:B thin films, where (002) is the predominant peak. Texture coefficient corresponding to (002) peak increases with B concentration from 0.50 to 1.00 at%. Crystallite size is found between 22 and 64nm. Nanofibrous surface morphology is observed in the field emission scanning electron microscopic images of ZnO:B thin films. The average nanofiber thickness value varies from 198 to 498nm. Atomic force microscopic images show the nanotip-like topology of ZnO:B thin films. The average surface roughnesses of the films are found in the range of 2.99-12.45nm. ZnO:B thin films are found to be highly transparent between visible to near infrared region of the electromagnetic spectrum. The highest transmittance of 87% is noticed for the 1.00 at% ZnO:B thin film prepared at the T-S of 450 degrees C. Optical band gaps of ZnO:B thin films vary between 3.15 and 3.31eV. 1.00 at% ZnO:B thin films prepared at various T-S show lower values of the band gap, refractive index and extinction coefficient at the photon wavelength of 750nm. Electrical resistivity of ZnO:B thin films are found to be between 0.25x10(4) and 1.39x10(4) m. 1.00 at% ZnO:B thin films prepared at various T-S show less electrical resistivity. Arrhenius plots of ZnO:B thin films prepared at various T-S show two conduction regions and activation energies of ZnO:B thin films are higher for the films deposited at lower T-S. ZnO:B thin films show n-type conductivity and carrier concentration increases with the increase of B concentration.