Optical band gap energy and urbach tail of CdS:Pb2+thin films

PbS-doped CdS nanomaterials were successfully synthetized using chemical bath. Transmittance measurements were used to estimate the optical band gap energy. Tailing in the band gap was observed and found to obey Urbach rule. The diffraction X-ray (XRD) show that the size of cristallites is in the similar to 33 nm to 12 nm range. The peaks belonging to primary phase are identified at 2 theta = 26.5v and 2 theta = 26.00 degrees corresponding to CdS and PbS respectively. Thus, a shift in maximum intensity peak from 2 theta = 26.4 degrees to 28.2 degrees is clear indication of possible transformation of cubic to hexagonal phase. Also peaks at 2 theta = 13.57 degrees, 15.9 degrees correspond to lead perchlorate thiourea. The effects on films thickness and substrate doping on the band gap energy and the width on tail were investigated. Increasing doping give rise to a shift in optical absorption edge similar to 0.4 eV.