Structural and transport characteristics of HgxCd1-xS thin composite films : A correlation

Abstract

Thin films of HgxCd1-xS for 0 < x < 0.25 were deposited by a chemical bath deposition technique onto the optically plane glass. The EDS studies showed that Cd2+ is replaced from the lattice by the Hg2+ ions during film growth. The crystallographic structure of these composites was determined by the X- Ray diffraction studies in the 2 range from 100 to 800 (CuKa - radiation). It appeared that the composites are polycrystalline of hexagonal wurtzite type with dominant reflections at d = 3.367 A0 (002), 3.160 A0 (101), 2.068 A0 (110) and 1.761 A0 (112). Both d and I / Imax for (002) and (101) change with the composition parameter x. It has also been noted that changes in d and I / Imax are continuous up to a value of x equal to 0.08. The crystallite size varied from 134 A0 to 180A0 for the range studied. The optical gaps were computed for these composites form the optical absorption measurements. The optical gap is of the direct type and decreases continuously from 2.42 eV to 1.75 eV for the change of x values from 0.01 to 0.08. A solid solution of the type HgxCd1-xS is therefore said to be formed in this range only. The dc electrical conductivities of these thin composite films were measured in the 300K - 550K temperature range. The materials exhibited n - type conduction. The electrical conductivity is found to be increased quasilinearly with the addition of Hg content in CdS. The materials transport characteristics such as activation energies in both high and low temperature regions, location of donor levels, intercrystalline barrier potentials, conduction mechanisms etc have been discussed. The changes in structural characteristics etc have been correlated with the observed transport properties.