Effect of fluorine doping on semiconductor to metal-like transition and optical properties of cadmium oxide thin films deposited by sol-gel process

Highly conducting fluorine doped n- type cadmium oxide thin films have been synthesized by sol-gel dip coating process on glass and Si substrates for various fluorine concentrations in the films. X-ray diffraction pattern confirmed the cubic CdO phase formation and SEM micrograph showed fine particles of CdO with size similar to 0.3 mu m. F concentration in the films was varied from 1.8% to 18.7% as determined from energy dispersive X-ray analysis ( EDX). The resistivity of the CdO films decreased with increase of F doping and increase of temperature below 14.6% of F, as usual for semiconductors. Above this F concentration the resistivity increased with increase of temperature like metals. Hall measurement showed very high carrier concentrations in the films lying in the range of similar to 2.93 x 10(20) cm(-3) to 4.56 x 10(21) cm(-3). UV- VIS- NIR spectrum of the films showed the optical bandgap energy increased with increase of F doping and corresponding carrier concentrations obtained from Burstein- Moss shift also support the Hall measurement results.