STUDIES OF THE GRAIN-BOUNDARY EFFECT IN ELECTRODEPOSITED CADMIUM TELLURIDE FILMS FROM OPTICAL MEASUREMENTS

Polycrystalline CdTe films were deposited onto SnO2 coated glass substrates using the electrodeposition technique with different deposition potentials, ranging from -670 to -725 mV, with respect to a saturated calomel electrode (SCE). The effect of the intercrystalline barrier on the carrier transport in CdTe films has been critically studied. The grain boundary potential (E(b)), the density of trap states at the intercrystalline boundary (Q(t)) and the carrier concentration (p) in the films were obtained. The surface roughness (sigma(0)) of the films was determined by utilising reflectance measurements while the band gap (similar to 1.49 eV) was determined from transmittance vs wavelength traces. The barrier height in the CdTe films was found to increase from 0.23 eV to 0.25 eV with the variation of the deposition potential from -675 to -725 mV; while the corresponding variation in the density of trap states at the grain boundary region was 1.0 x 10(12) - 2.1 x 10(12) Cm-2. The carrier concentration in such highly resistive films (10(4) Omega-cm) was obtained from the experimental values of the Debye length, determined from the optical transmittance measurements.