Thickness dependent electrical properties of CdO thin films prepared by spray pyrolysis method

A large number of thin films of cadmium oxide have been prepared on glass s ubstrates by spray pyrolysis method. The prepared films have uniform thickn ess varying from 200-600 nm and good adherence to the glass substrate. A sy stematic study has been made on the influence of thickness on resistivity, sheet resistance, carrier concentration and mobility of the films. The resi stivity, sheet resistance, carrier concentration and mobility values varied from 1.56-5.72x10(-3) Omega-cm, 128-189 Omega/square, 1.6-3.9x10(21) cm(-3 ) and 0.3-3 cm(2)/Vs, respectively for varying film thicknesses. A systemat ic increase in mobility with grain size clearly indicates the reduction of overall scattering of charge carriers at the grain boundaries. The large co ncentration of charge carriers and low mobility values have been attributed to the presence of Cd as an impurity in CdO microcrystallites. Using the o ptical transmission data, the band gap was estimated and found to vary from 2.20-2.42 eV. These films have transmittance around 77% and average reflec tance is below 2.6% in the spectral range 350-850 nm. The films are n-type and polycrystalline in nature. SEM micrographs of the CdO films were taken and the films exhibit clear grains and grain boundary formation at a substr ate temperature as low as 523 K.