Single solid source precursor route to the synthesis of MOCVD Cu-Cd-S thin films

Abstract

Bis-(morpholinodithiato-s,s')-Cu-Cd was synthesized from appropriate reagents as a single solid source precursor and characterized using particle induced x-ray emission (PIXE), Fourier transform infrared (FTIR) spectroscopy and differential thermal analysis (DTA). Cu-Cd-S thin films were deposited on sodalime glass substrate using MOCVD technique at temperatures in the range 360 °C–450 °C. The films were further characterized using Rutherford backscattering spectroscopy (RBS), x-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible spectroscopy and four-point probe technique. PIXE revealed that the synthesized precursor contained the expected elements which led to the successful deposition of the Cu-Cd-S thin films. FTIR ascertained that the organic ligand actually attached to the metals. DTA analysis showed that the synthesized precursor was thermally stable and could pyrolyzed around 300 and 500 °C. RBS of the deposited films showed that the stoichiometry and the thickness depended on deposition temperature. XRD analysis revealed that the films deposited at 360 and 380 °C are amorphous while those deposited at 400 °C to 450 °C showed peaks, which supported the possible co-existence of CuS and CdS as Cu-Cd-S, with an improvement in the crystallinity as substrate temperature increased. SEM showed that the films are uniform and crack-free, in which the morphology strongly depended on substrate temperature. Optical analysis revealed that the films have high absorbance in the UV region and high transmittance in the visible and near infrared region, in which direct band gap energy of 2.36 to 2.14 eV was obtained as deposition temperature increased. Other optical parameters such as Urbach energy, refractive index, extinction coefficient, dielectric constant also increased as the deposition temperature increased. Electrical analysis showed that resistivity is temperature dependent as it reduced as deposition temperature increased.