Compositional, Structural, Morphological, Optical and Electrical Property Evolutions in MOCVD Cu-Zn-S Thin Films Prepared at Different Temperatures Using a Single Solid Source Precursor

Abstract

Bis-(morpholinodithiato-s,s′)-Cu-Zn was synthesized as a single solid source precursor and characterized using particle-induced x-ray emission (PIXE), Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). Cu-Zn-S thin film was deposited on sodalime glass substrate using metal organic chemical vapor deposition (MOCVD) technique at temperatures ranging from 360°C to 450°C. The thin films were characterized using Rutherford backscattering spectroscopy (RBS), x-ray diffraction (XRD), scanning electron microscopy (SEM), UV–visible spectroscopy and four-point probe technique. PIXE of the precursor confirmed the presence of the expected elements that can lead to deposition of Cu-Zn-S thin film while FTIR confirmed that the organic ligands were attached to the metals. DSC showed that the precursor is thermally stable and can pyrolyze at temperature between 340°C and 460°C. RBS analysis of the films showed that there was no substantial deposition at 360°C while other films showed various stoichiometry and thickness. XRD analysis of the films showed that films deposited at 360°C and 380°C are amorphous, while those deposited between 400°C and 450°C showed peaks, in which the crystal size decreased as the deposition temperature increased. The SEM micrographs showed that the morphology of the films is temperature dependent and as deposition temperature increased larger secondary grains dissociated into smaller grains that are closely packed, without cracks and holes. Optical characterization showed that the films exhibited high transmittance, which fairly increased as the deposition temperature increased. A direct band gap value between 2.49 eV and 2.92 eV was obtained as deposition temperature increased. Urbach energy also increased from 0.87 eV to 1.51 eV, while the steepness parameter decreased as the deposition temperature increased. The electrical characterization showed that the resistivity of the films decreased as the deposition temperature increased while the I–V plot showed a rectifying character.