Effect of cadmium sulfide thickness on electron beam-deposited titania/cadmium sulfide nanocomposite films

摘要

Improving the photo-catalytic response of TiO_2 semiconductor nanocomposites to visible light is the key issue. Heterogeneous TiO_2/CdS nanocomposite films (NCFs) are successfully deposited on the p-type [110] silicon substrate using an electron beam deposition (EBD) method. We report for the first time CdS thickness dependent photocurrent response of such NCFs. Effects of varying CdS thicknesses (50-150 nm) on the structural, optical and electrical properties are examined. The lattice parameters and nanocrystallinity of these NCFs obtained from XRD measurement show gradual increment with increase of CdS thickness and preferably grow along (101), (112) and (200) directions for various CdS thicknesses. The calculated value of mean lattice parameters and volume is a=0.371 nm, c=0.945 nm and V=13.73 nm~3 respectively. The estimated average crystallite sizes for TiO_2 and TiO_2/CdS NCFs at various CdS thicknesses are 12.3, 24.9, 39.59 and 42.4 nm. Interestingly, the FES EM images reveal clusters-like growth pattern attributed to the mechanism of particles agglomeration towards free energy minimization. The UV-vis reflectance in the range of 350 to 700 nm decreases due to the introduction of CdS in the NCF due to increased visible absorption. The TiO_2/Si and CdS/Ti02/Si heterojunction exhibits a rectifying behavior with considerably high photocurrent contrast and fast responses to visible light due to enhanced light absorption. The dark current increases significantly with increasing CdS thickness due to increase in grain size. Our results suggest that the structural and optoelectronic properties of TiO_2 films can significantly be improved by varying the thicknesses of CdS film useful for nanophotonics.