Photoconductivity and Thermoelectric Power of Zn_xCd_1-xSe Films

Zn_xCd_1-xSe (0≤x≤1) films were deposited by two zone hot wall evaporation technique. X-ray diffraction analysis of the films indicated a predominant wurtzite structure for x<0.5, which changed to zinc blende structure for x>0.7. The films had a mixed structure for 0.5<x<0.7. The films were highly resistive (resistivity varying within 3 Ω· cm to 1.5×10⁵ Ω· cm for 0≤x≤1.0) with partially depleted grains. The optical band gap (E _g), determined from the reflectance measurements, indicated a direct transition with a bowing effect in E _g versus x plot. The conductivity at low temperature (for x<0.6) could be explained by thermionic emission over the intercrystalline barrier, while for higher x quantum mechanical tunneling through the barrier became predominant. The variation of the barrier height (E _bd) with the intensity of illumination was obtained from the photoconductivity measurements. The majority carrier capture cross-section ( 1-4×10^-18 cm²) of the grain boundary traps ( 1×10¹¹-1×10¹² cm^-2) was determined. The effect of the intercrystalline barrier on the thermoelectric power measurements was also considered.