Study on structure and optical properties of Bi_2O_3 thin films prepared by reactive pulsed laser deposition

摘要

Bi_2O_3 thin films were prepared onto glass substrates by pulsed laser deposition (PLD) at different O_2 pressures and substrate temperatures. The crystallinity, phase structure, grain size and surface roughness of PLD thin films were investigated by X-ray diffraction (XRD) and scanning probe microscopy (SPM) techniques, respectively. The optical transmission spectra of films were examined in order to study their energy gap. The results showed that the phases of obtained films were β-Bi_2O_3 and/or δ-Bi_2O_3, and their preferred orientation was (201) and (111), respectively; the average grain size and the surface roughness of films ranged from 20 nm to 120 nm and from 0.8 nm to 16 nm, respectively, depending on the preparing conditions. At different oxygen pressures (0.15-45 Pa), two energy gaps (E_g) of films were found, and their values were about 3.5 eV and 2.88 eV, respectively. At substrate temperatures of 75 ℃, 200 ℃ and 500 ℃, only one energy gap was obtained, and it decreased significantly from 3.72 eV to 3.25 eV with increasing substrate temperature from 75 ℃ to 500 ℃. The difference in the values of energy gap of investigated films can be mainly correlated with the phase composition of respective films.