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.