Morphological and electrical characterization of Cu-doped PbS thin films with AFM

Illia Dobryden^{1, 2}, Baligh Touati³, Abdelaziz Gassoumi^3,4, Alberto Vomiero¹,Najoua Kamoun³, Nils Almqvist^1*

¹Department of Engineering Sciences and Mathematics, Division of Materials Science/Experimental Physics, Luleå University of Technology, Luleå, SE-971 87, Sweden

²Department of Chemistry, Division of Surface and Corrosion Science, KTH Royal Institute of Technology, Stockholm, SE-100 44, Sweden

³Physics Condensed Matter Laboratory, Faculty of Science of Tunis, University of Tunis El-Manar, Tunis, 2092, Tunisia

⁴King Khalid University, College of Science, Physics Department, P.O. Box 9004, Abha 61413, Saudi Arabia

Adv. Mater. Lett., 2017, 8 (11), pp 1029-1037

DOI: 10.5185/amlett.2017.1545

Publication Date (Web): Aug 05, 2017

E-mail: nils.almqvist@ltu.se

Full Article

Abstract

Lead sulphide (PbS) is a direct band gap IV–VI intrinsic p-type semiconductor with good potential for application in solar cells, sensors, etc. Doping the films with Cu²⁺ ions may improve the electrical properties. Here, Cu-doped PbS films were deposited on conducting glass substrates. The morphology, topography and thickness of the doped PbS films were examined using atomic force microscopy (AFM) and high-resolution SEM. AFM analysis showed decreasing surface roughness and grain size with the increase of Cu²⁺ concentration from 0.5 to 2.0 at%. Local surface electrical measurements using conducting AFM and Kelvin probe force microscopy showed the possibility to probe semi-quantitatively the changes in surface potential, work function, and Fermi level upon doping of the films. The estimated apparent work function for the un-doped PbS grains in the film was slightly above 4.5 eV, while it decreased to a minimum value of 4.43-4.45 eV at 1–1.5 at% Cu-doping. Conducting AFM measurements showed that local resistance of the doped samples is lower than on pure PbS films. These results indicate Cu doping as an effective strategy to tune the electrical properties of PbS thin films toward the development of suitable optically active materials for application in photovoltaics.