Vertical 2D/3D Semiconductor Heterostructures Based on Epitaxial Molybdenum Disulfide and Gallium Nitride

When designing semiconductor heterostructures, it is expected that epitaxial alignment will facilitate low-defect interfaces and efficient vertical transport. Here, we report lattice-matched epitaxial growth of molybdenum disulfide (MoS<sub>2</sub>) directly on gallium nitride (GaN), resulting in high-quality, unstrained, single-layer MoS<sub>2</sub> with strict registry to the GaN lattice. These results present a promising path toward the implementation of high-performance electronic devices based on 2D/3D vertical heterostructures, where each of the 3D and 2D semiconductors is both a template for subsequent epitaxial growth and an active component of the device. The MoS<sub>2</sub> monolayer triangles average 1 μm along each side, with monolayer blankets (merged triangles) exhibiting properties similar to that of single-crystal MoS<sub>2</sub> sheets. Photoluminescence, Raman, atomic force microscopy, and X-ray photoelectron spectroscopy analyses identified monolayer MoS<sub>2</sub> with a prominent 20-fold enhancement of photoluminescence in the center regions of larger triangles. The MoS<sub>2</sub>/GaN structures are shown to electrically conduct in the out-of-plane direction, confirming the potential of directly synthesized 2D/3D semiconductor heterostructures for vertical current flow. Finally, we estimate a MoS<sub>2</sub>/GaN contact resistivity to be less than 4 Ω·cm<sup>2</sup> and current spreading in the MoS<sub>2</sub> monolayer of approximately 1 μm in diameter.