Study of valence band tailing effect induced by electronic excitations in nanocrystalline cadmium oxide thin films.

Nanocrystalline Cadmium oxide (nc-CdO) thin films were deposited on indium tin oxide (ITO) coated glass substrates by the sol–gel spin coating technique. The prepared films were irradiated with energetic ions for two different fluences for inducing electronic excitations and/or ionizations. Films are investigated for structural studies using grazing incidence X-ray diffraction (GIXRD) and for optical studies by UV–vis absorption spectroscopy. The structural study reveals that the films are polycrystalline in nature with cubic phase and the average crystallite size is in the range 24–27 nm, which exhibit insignificant change upon irradiation. However, films show an increase in the band gap from 2.58 ± 0.02 to 2.72 ± 0.02 eV with increasing in the ion fluence. The initial high value of the band gap is attributed to Burstein–Moss (BM) shift, while the increase in band gap upon irradiation is explained by disorder induced valence band tailing states created by high density of electronic excitations in the lattice. [ABSTRACT FROM AUTHOR]