Atmospheric pressure MOCVD of highly conductive thin films of CdO

Abstract

Thin conducting oxides (TCOs) are used in a variety of applications such as thin film solar cell technology (for front contacts and window layers) and applications such as gas sensors and functional glass windows [1−3]. To be competitive, the films have to be of high quality in terms of optical transmission and electrical conductivity. In this study, atmospheric pressure MOCVD (metal organic chemical vapour deposition) of CdO thin films have been deposited using a novel oxygen precursor. Alcohols have been used successfully for deposition of ZnO, avoiding the gas phase pre−reaction between the zinc precursor and oxygen or water vapour [4]. An alcohol source, when dry, can prevent unwanted pre−reactions with the cadmium precursor, dimethylcadmium (Me2 Cd). CdO films were deposited in a purpose designed MOCVD reactor. A horizontal reactor cell was maintained at atmospheric pressure and a resistive heater was used to heat the substrate in the range 250−310 oC. The precursors were dimethylcadmium (Me2 Cd), adduct grade, supplied by Epichem Ltd., and for the novel oxygen source: n−butanol (99.8% anhydrous), supplied by Aldrich. The thin film growth was monitored by an in−situ laser interferometer using a 635 nm. This monitoring gave accurate measurement of thickness during growth and information about the film properties such as the reflectance and roughening.