Structural and Esaki-Diode-like Electrical Properties of PLD-Grown 2D MoS2 Film on MBE Grown AlN/Si(111) Heterostructures

MoS2 thin films were synthesized via pulsed laser deposition (PLD) onto AlN/Si(111) templates, where the AlN buffer layers (110 and 200 nm thick) were grown by molecular beam epitaxy. We achieved excellent MoS2 thickness uniformity (≈3 monolayers) and confirmed the conformal coverage of the PLD-grown films by Raman mapping. Transmission electron microscopy analysis confirmed the epitaxial character of the AlN film and the presence of an ultrathin aluminum oxynitride layer on its surface. Following X-ray photoelectron spectroscopy analysis, oxygen impurities were confirmed in the bulk AlN film as well. Heterojunctions between the ultrathin MoS2 film and AlN, investigated by current-voltage characterization of vertical diode structures, exhibit Esaki-diode-like behavior with a negative-resistance zone. A diagram of the energy bands and Fermi levels in the heterostructure composed of the thick oxygen-doped AlN film sandwiched between the MoS2 and Si electrodes was proposed, and the observed Esaki-diode-like current-voltage characteristic was attributed to electron tunneling from the oxygen impurity band in the AlN film into the valence band of the degenerate p-MoS2 film.