Photoconductivity and Thermoelectric Power of ZnxCd1-xSe Films

Abstract

Znx Cd1-x Se (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.