Pulsed chemical vapor deposition of Cu 2 S into a porous TiO 2 matrix

• Published in: Journal of vacuum science & technology. A, Vacuum, surfaces, and films Vacuum, surfaces, and films, 2011-07, Vol.29 (5), p.051505-051505-5
• Main Authors: Carbone, I., Zhou, Q., Vollbrecht, B., Yang, L., Medling, S., Bezryadina, A., Bridges, F., Alers, G. B., Norman, J. T., Kinmen, T.
• Format: Article
• ISSN: 0734-2101; 1520-8559
• DOI: 10.1116/1.3609772

Chalcocite (Cu 2 S) has been deposited via pulsed chemical vapor deposition (PCVD) into a porous TiO 2 matrix using hydrogen sulfide and a metal-organic precursor. The precursor used is similar to the more common Cu(hfac)(tmvs) precursor, but it is fluorine free and exhibits increased thermal stability. The simultaneous exposure of the substrate to the copper precursor and hydrogen sulfide resulted in nonuniform Cu 2 S films with a temperature independent deposition rate implying gas phase reaction kinetics. The exposure of mesoporous TiO 2 and planar ZnO to alternating cycles of the copper precursor and hydrogen sulfide resulted in a PCVD film that penetrated fully into the porous TiO 2 layer with a constant deposition rate of 0.08 nm/cycle over a temperature range of 150-400°C. The chalcocite (Cu 2 S) stoichiometry was confirmed with extended x-ray absorption fine structure measurements (EXAFS) and x-ray photoelectron spectroscopy. Calculations of the EXAFS spectrum for different Cu x S phases show that EXAFS is sensitive to the different phase stoichiometries. Optical absorption measurements of CVD thin films using photothermal deflection spectroscopy show the presence of a metallic copper-poor phase for gas phase nucleated films less than 100 nm thick and a copper-rich semiconducting phase for thicknesses greater than 100 nm with a direct band gap of 1.8 eV and an indirect bandgap of 1.2 eV.