Epitaxial Molybdenum Disulfide/Gallium Nitride Junctions: Low-Knee-Voltage Schottky-Diode Behavior at Optimized Interfaces

Low turn-on (knee) voltage (∼0.3 V) Schottky-diode behavior of a four-layer (4L) MoS₂/GaN junction is achieved by optimizing the in situ interface preparation of the GaN substrate prior to MoS₂ overlayer growth in a vacuum system using metallic molybdenum and hydrogen sulfide gas as precursors. The process leads to a clean nitrogen-terminated GaN surface that bonds well to the MoS₂ film revealing a 2 × 2 reconstruction at the interface observed in low-energy electron diffraction (LEED). Atomic force microscopy and X-ray photoelectron spectroscopy provide clear images of the GaN terraces through the MoS₂ overlayer confirming close adhesion and absence of oxygen and other contaminants. Density functional theory calculations predict the formation of the 2 × 2 superstructure at a clean interface. Transport measurements show diode behavior at an on/off ratio of ∼10⁵ for ±1 V with a forward direction for the positive voltage applied to the MoS₂ layer. Combining transport and photoelectron spectroscopy measurements with theory, we deduce a Fermi-level position in the MoS₂ gap consistent with interface charge transfer from MoS₂ to the substrate. The high performance of the MoS₂/Gan diode highlights the technological potential of devices based on GaN/MoS₂ interfaces.