A photoemission study of barrier and transport properties of the interfaces of Au and Cu with WSe 2(0001) surfaces

Abstract

The interface formation of gold and copper with UHV-cleaved WSe 2(0001) van der Waals-surfaces has been studied by photoelectron spectroscopy using synchrotron radiation and He I excitation. The metal films were evaporated on samples kept at room temperature and at T = 85 K, respectively. No interface reactions have been observed. Metal films show three-dimensional island growth at room temperature and continuous layer growth at 85 K. The Schottky barrier heights are determined to be Φ Bp = 0.76 ± 0.02 eV for Au - and Φ Bp = 1.0 ± 0.02 eV for Cu p-WSe2 , respectively. Temperature-depende photovoltages were measured to determine the dominant contributions to the charge transport across the interfaces. For the Au-contact the photovoltages induced by the helium lamp can be calculated assuming simple thermionic emission which allows an independent measurement of the barrier height. The Cu-contacts show a significant reduction of photovoltages which is discussed in terms of interface reactions and diffusion of Cu into the space-charge region. Non-equilibrium characterization with photoelectron spectroscopy is shown to be very useful to optimize the parameters for interface preparation.