Structural and optoelectronic properties of antimony incorporated tin oxide thin films

Thin films of undoped and antimony doped tin oxide (SnO2 and Sb:SnO2) prepared by spray pyrolysis technique with different antimony concentrations are found to be polycrystalline with tetragonal crystal structure, having preferential growth along the (2 1 1) and (1 1 2) planes. Randomly oriented needle-shaped polyhedron like grains are observed in the FE-SEM images owing to large scattering effect in the films. From X-ray photoelectron spectroscopy (XPS) measurement, it is observed that films are oxygen deficient. Concentration of Sb in the SnO2 films is slightly less than that of starting solution. Valence states for Sn, Sb and O, observed from the XPS measurement are Sn4+, Sb5+/Sb3+ and O22−O22−, respectively. The direct optical band gap (Eg) has increased from 3.55 (undoped) to 3.60 eV with Sb concentration showing formation of degenerate semiconductor. The strong violet and comparatively weak red emissions have observed in room temperature photoluminescence (PL). The origin of various peaks in PL spectra can be assigned to the combined effect of oxygen vacancies, tin interstitials or dangling bonds, singly charged oxygen vacancies, interstitial oxygen and crystal defects present in the films. The films deposited with 2 at.% Sb exhibited lowest value of resistivity (1.22 × 10−3 Ω cm) and highest value of carrier concentration (5.19 × 1020 cm−3), mobility (9.83 cm2 V−1 s−1) and figure of merit (2.11 × 10−3 Ω−1).