Tuning the physical properties of spray pyrolysed nanocrystalline CdO thin films by varying the substrate temperature

S. J. Helen; Suganthi Devadason; M. Haris; T Mahalingam; Rathinam Chandramohan; S. R. Srikumar

Abstract

Spray pyrolysis technique has been employed to deposit cadmium oxide (CdO) thin films on glass substrates preheated to different temperatures (250, 350, 400 and 500°C). Structural, morphological, optical and electrical characterization studies were performed on the films to study the behavior of the films. The thicknesses of the films prepared at different substrate temperatures vary from 497 to 465 nm. X-ray diffraction analysis reveals that the films are polycrystalline exhibiting cubic structure of lattice constant, 4.693Å. Scanning electron microscopic images illustrate that the thin films show spherical shaped agglomerated grains of bigger dimension (few μm). The elemental analysis supports the good stoichiometry of films with the elemental composition of cadmium and oxygen as 49 and 51%, respectively. The optical spectra record a high transmittance value (70~80%) in the non-absorption region for the incident visible and infrared light. The optical band gaps of CdO films determined from the transmission spectra range from 2.34 to 2.44 eV for films prepared at different substrate temperature. Photoluminescence spectra show the characteristic near band emission peaks of CdO centered around 500 nm. The electrical studies using Hall effect and I-V measurements bring out the important feature of high conductivity which is further found to improve on the illumination of CdO films. The results suggest that the films prepared at 350 and 400°C are more suitable for optoelectronic applications due to their high electrical conductivity and optical transmittance in the visible region of sunlight.

Abstract

Keywords