Crystallographic plane and topography-dependent growth of semipolar InGaN nanorods on patterned sapphire substrates by molecular beam epitaxy

Insight into the Ga/In flux ratio and crystallographic plane dependence of MBE self-assembled growth of InGaN nanorods on patterned sapphire substrates

A controllable self-assembled growth using molecular beam epitaxy (MBE) of dense, uniform, and high-aspect-ratio InGaN nanorods (NRs) is achieved through regulating the Ga/In flux ratio and employing high Miller index planes of patterned sapphire substrates (PSSs). It is clearly demonstrated that both the low Ga/In flux ratio and high Miller index plane of PSS patterns facilitate the three-dimensional growth mode for InGaN NRs and simultaneously suppress NR coalescence. A lower Ga/In flux ratio favors a higher density, a larger aspect ratio, and a smaller coalescence degree of InGaN NRs through enhancing axial growth and inversely suppressing radial growth. The specific surface structures of high Miller index planes, e.g., the well-organized step-terrace and irregular bulge structures, critically affect the morphology, dimensions, density, and crystallographic orientation of MBE self-assembled NRs. In particular, the narrow and ordered step-terrace structure in the C₃-plane-(4 5[combining macron] 1 38) plane-on a hexagonal pyramid favors the highest density, largest aspect ratio, and best uniformity of semipolar InGaN NRs, thus contributing to optimal photoluminescence performance. A thorough understanding of the mechanism of the effect of the Ga/In flux ratio and crystallographic plane on the MBE self-assembled growth behaviour of InGaN NRs was gained through experimental and theoretical exploration. This work contributes towards a deep understanding of the MBE self-assembled growth mechanism and controllable fabrication of dense, well-separated, and uniform InGaN NRs, thus contributing to the enhanced performance of NR-based optoelectronic devices.

High-quality epitaxial wurtzite structured InAs nanosheets grown in MBE

In this study, we have grown epitaxial wurtzite structured InAs nanosheets using Au catalysts on a GaAs{111}_B substrate by molecular beam epitaxy. Through detailed electron microscopy characterization studies on grown nanosheets, it was found that these wurtzite structured InAs nanosheets grew epitaxially on the GaAs{111}_B substrate, with {0001[combining macron]} catalyst/nanosheet interfaces and extensive {112[combining macron]0} surfaces. It was anticipated that the epitaxially grown InAs nanosheet can be triggered by a high supersaturation in catalysts, leading to an inclined growth leaving the substrate surface, and driven by the small lattice mismatch between the nanosheets and the substrate, with the orientation relationship of (0001[combining macron])_InAs//(112[combining macron])_GaAs. This study provides insights into achieving epitaxial free-standing III-V nanosheet growth.

Spatially controlled VLS epitaxy of gallium arsenide nanowires on gallium nitride layers

MOVPE of Au catalyzed p-GaAs nanowires on n-GaN layers. Left: VLS growth optimization (density and morphology). Middle and right: site-controlled pn-junctions by lateral and vertical anisotropic NWs in structured SiOx openings (scalebar 1 μm).

Self-Integrated Hybrid Ultraviolet Photodetectors Based on the Vertically Aligned InGaN Nanorod Array Assembly on Graphene

Integration of one-dimensional (1D) semiconductors with two-dimensional (2D) materials into hybrid systems is identified as promising applications for new optoelectronic and photodetection devices. Herein, a self-integrated hybrid ultraviolet (UV) photodetector based on InGaN nanorod arrays (NRAs) sandwiched between transparent top and back graphene contacts forming a Schottky junction has been demonstrated for the first time. The controlled van der Waals epitaxy of the vertically aligned InGaN NRA assembly on graphene-on-Si substrates is achieved by plasma-assisted molecular beam epitaxy. Moreover, the self-assembly formation mechanisms of InGaN NRAs on graphene are clarified by theoretical calculations with first-principles calculations based on density functional theory. The peculiar 1D/2D heterostructure hybrid system-based integrated UV photodetector simultaneously exhibits ultrafast response time (∼50 μs) and superhigh photosensitivity (∼10⁵ A/W). It is highly believed that the concept proposed in this work has a great potential and can be widely applied for the next-generation integrated 1D/2D nano-based optoelectronic and photodetection devices.