Determination of the transport parameters of nanocrystalline CdSe:Cu thin films

Abstract

Thin films of copper (Cu)-doped CdSe are prepared by the physical vapor deposition technique. X-ray diffraction analysis shows that the films crystallize in hexagonal structure with (100) as the preferred orientation. Scanning electron microscope studies reveal that the grains are spherical in shape and uniformly distributed all over the surface of the substrates. The transport properties of Cu-doped CdSe thin films have been investigated by the time-of-flight measurement, steady-state photocarrier grating and steady-state photoconductivity techniques. The temperature dependence of dark conductivity and photoconductivity data reflects the existence of two independent donor energy levels. The bimolecular recombination nature of the thin films has been found from the photocurrent-illumination dependence at different applied voltages. The minority carrier diffusion length (Ldiff) is obtained both from the best fit of the experimental photocurrent ratio β versus grating period (Λ) and from the ‘Balberg plot’. A straight line has been obtained from the best fit, which confirms that the measured length is the ambipolar diffusion length.