Growth and extrinsic p-type doping of pulsed laser deposited few layer WS2 films

U.P. Rathod, C. Iheomamere, C.L. Arnold, A.A. Voevodin, N.D. Shepherd
University of North Texas,
United States

Keywords: 2D materals, PLD, electrical properties

Summary:

X-ray photoelectron, Raman and diffraction studies of few-layered pulsed laser deposited (PLD) WS2 films performed as a function of laser fluence and frequency suggest that Volmer-Weber island growth is dominant for the growth conditions investigated. The correlations between structure, Hall mobility, and Fermi level positions indicate that reducing chalcogen vacancies is critical for optimal mobility in transition metal dichalcogenide (TMD) semiconductors. Extrinsic p-type doping of few-layered TMD WS2 films with Nb via pulsed laser deposition is demonstrated. Ultraviolet photoelectron spectroscopy (UPS) studies showed a Fermi level of 1.41 eV from the valence band edge for the n-type controls. Films doped at 0.5 and 1.1 atomic percentages niobium were p-type and characterized by Fermi levels at 0.31 eV and 0.18 eV from the valence band edge. That is, the Fermi level moved closer to the valence band edge with increased doping. With increased Nb doping, the hole concentrations increased from 3.9x1012 to 8.6x1013 cm-2. X-ray photoelectron spectroscopy indicates that Nb substitutes on W lattice sites, and the measured peak shifts toward lower binding energy corresponded well with the UPS data. Schematic energy band diagrams are proposed. The approach demonstrates the potential of PLD for targeted doping of transition metal dichalcogenides, and by extension, its potential for creating p-n junctions.