Abstract
Van der Waals epitaxial GaN thin films on c-sapphire substrates with a sp2-bonded two-dimensional (2D) MoS2 buffer layer, prepared by pulse laser deposition, were investigated. Low temperature plasma-assisted molecular beam epitaxy (MBE) was successfully employed for the deposition of uniform and ~5 nm GaN thin films on layered 2D MoS2 at different substrate temperatures of 500, 600 and 700 °C, respectively. The surface morphology, surface chemical composition, crystal microstructure, and optical properties of the GaN thin films were identified experimentally by using both in situ and ex situ characterizations. During the MBE growth with a higher substrate temperature, the increased surface migration of atoms contributed to a better formation of the GaN/MoS2 heteroepitaxial structure. Therefore, the crystallinity and optical properties of GaN thin films can obviously be enhanced via the high temperature growth. Likewise, the surface morphology of GaN films can achieve a smoother and more stable chemical composition. Finally, due to the van der Waals bonding, the exfoliation of the heterostructure GaN/MoS2 can also be conducted and investigated by transmission electron microscopy. The largest granular structure with good crystallinity of the GaN thin films can be observed in the case of the high-temperature growth at 700 °C.
Highlights
Published: 26 May 2021At present, advanced applications of optoelectronic and electronic devices have attracted considerable interest for utilization on flexible and wearable devices for displays, solar cells, and detectors [1,2]
The many excellent properties of gallium nitride (GaN) can provide chemical and mechanical stability, such as good electron-mobility, direct bandgap, thermal stability, and better conductivity [5]. It has been utilized for the primary layers of heterostructure films for several applications, such as GaN-based high electron mobility transistors (HEMTs), light emitting diodes (LEDs), and UV photo-detectors [6,7,8]
The pressure of nitrogen plasma was fixed at 9.7 × 10−5 Torr, and the temperature of Ga K-cell was controlled at 800 ◦ C in the beam equivalent pressure of 6 × 10−8 Torr
Summary
At present, advanced applications of optoelectronic and electronic devices have attracted considerable interest for utilization on flexible and wearable devices for displays, solar cells, and detectors [1,2]. The many excellent properties of GaN can provide chemical and mechanical stability, such as good electron-mobility, direct bandgap, thermal stability, and better conductivity [5] It has been utilized for the primary layers of heterostructure films for several applications, such as GaN-based high electron mobility transistors (HEMTs), light emitting diodes (LEDs), and UV photo-detectors [6,7,8]. Transition metal dichalcogenides (TMDs) based on semiconductor materials have attracted interest to be applied on 2D layer heterostructures with vdW epitaxial technique. The surface conditions of 2D MoS2 and vdW epitaxial GaN films were characterized by in situ monitoring equipment, including reflection high energy electron diffraction (RHEED) in the MBE system. The temperature effects on the growth mechanism of vdW epitaxial GaN/MoS2 was investigated in the report
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