研究目的
Investigating the van der Waals epitaxy of high-quality single-crystalline AlN and the demonstration of AlGaN tunnel junction deep-ultraviolet light-emitting diodes directly on graphene.
研究成果
The study successfully demonstrated the van der Waals epitaxy of high-quality single-crystalline AlN and AlGaN deep-UV LEDs on graphene using plasma-assisted MBE. The substrate/template beneath graphene plays a critical role in governing the initial AlN nucleation. The strong surface electrostatic potential of the underlying AlN template enables a large-scale parallel epitaxial relationship for AlN/graphene/AlN. The high-quality AlN grown on graphene was confirmed by the demonstration of AlGaN tunnel junction deep-UV LEDs operating at 260 nm, which exhibit a maximum external quantum efficiency of 4% for the direct on-wafer measurement.
研究不足
The study is limited by the initial nucleation behavior on graphene, which is influenced by the substrate/template beneath graphene. The inert surface of pristine graphene suppresses the nucleation of III-nitrides, which could limit the growth of high-quality continuous epilayers.
1：Experimental Design and Method Selection:
The study utilized plasma-assisted molecular beam epitaxy (MBE) for the van der Waals epitaxy of AlN on graphene. The initial AlN nucleation layer was grown using migration enhanced epitaxy (MEE), followed by the growth of a 500 nm AlN epilayer.
2：Sample Selection and Data Sources:
Commercial single monolayer graphene grown on Cu(111) by CVD was transferred onto sapphire and AlN template substrates.
3：List of Experimental Equipment and Materials:
A Veeco GENxplor MBE system equipped with a radio frequency (RF) plasma-assisted nitrogen source was used.
4：Experimental Procedures and Operational Workflow:
The graphene/substrates were baked and outgassed at 200°C and 600°C in the MBE load-lock chamber and preparation chamber for 2 h, respectively. The growth conditions included a nitrogen flow rate of
5：3 sccm, a RF plasma forward power of 350 W, an Al beam equivalent pressure (BEP) in the range of 0 × 10^-8 Torr to 0 × 10^-7 Torr, and a substrate temperature of 900°C. Data Analysis Methods:
The growth procedure was monitored in situ using reflection high energy electron diffraction (RHEED). The material quality was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy, X-ray diffraction (XRD), electron backscatter diffraction (EBSD), and scanning transmission electron microscopy (STEM).
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