  Electrical and optical characterization of two-dimensional/three-dimensional
(2D/3D) p-molybdenum disulfide/n-gallium nitride (p-MoS2/n-GaN) heterojunction
diodes are reported. Devices were fabricated on high-quality, large-area p-MoS2
grown by chemical vapor deposition (CVD) on hexagonal sapphire substrates. The
processed devices were transferred onto GaN/sapphire substrates, and the
transferred films were characterized by X-ray diffraction (XRD) and atomic
force microscopy (AFM). On-axis XRD spectra and surface topology obtained from
AFM scans were consistent with previously grown high-quality, continuous MoS2
films. Current-voltage measurements of these diodes exhibited excellent
rectification, and capacitance-voltage measurements were used to extract a
conduction band offset of approximately 0.2 eV for the transferred MoS2/GaN
heterojunction. This conduction band offset was confirmed by internal
photoemission (IPE) measurements. The energy band lineup of the MoS2/GaN
heterojunction is proposed here. This work demonstrates the potential of 2D/3D
heterojunctions for novel device applications.
