STUDY OF OPTICAL PROPERTIES OF CdS/PbS AND PbS/CdS HETEROJUNCTION THIN FILMS DEPOSITED USING SOLUTION GROWTH TECHNIQUE

Using solution growth technique, ternary stack thin films of CdS/PbS and PbS/CdS were deposited on plane glass substrates at room temperature. Both heterojunction films as well as their binary components: PbS and CdS, that make up the stacks were subjected to 300-900 nm range spectrophotometric analysis which provided the absorbance and transmittance data from which the absorption coefficient, alpha and other optical constants of the films were estimated. Structural characterization was also done on these films using X-ray diffraction which clearly showed nearly similar diffraction patterns and peaks for both heterojunction deposits. Direct bandgaps of 1.83eV, 2.55eV, 1.37eV and 2.35eV were obtained for PbS/CdS, CdS/PbS, PbS, and CdS deposits respectively while indirect band gap values of 1.72eV and 1.45eV were revealed for CdS/PbS and PbS/CdS stacks respectively. It is seen that whereas both heterojunction thin films differed in their band gaps, either value was closer to the band gap of the deposit binary film away from the substrate. Fairly steady refractive index of 2.5 for 170 nm thick PdS/CdS of 28.7nm crystal grain size and 2.6 for 154nm thick CdS/PbS of 30.1 nm grain size were revealed.