研究目的
To investigate the role of lattice matching in the coupling between two materials in vertical heterostructure (HS) by fabricating a heterojunction device with a few layers of p-type WSe2 and n-type MoSe2 with different crystal orientation angles.
研究成果
The study demonstrated that lattice matching plays a crucial role in the coupling between two materials in vertical heterostructures. The untwisted HS (0?) exhibited higher sensitivity under IR illumination, while the twisting effect was not noticeable under UV illumination. The twisted HS showed weak coupling due to lattice mismatch, as confirmed by photoluminescence and Raman spectroscopy. The findings highlight the importance of crystal orientation matching in vertical heterojunction devices for optoelectronic applications.
研究不足
The study is limited by the delicacy in fabrication of the HS device, which leads to large experimental errors. Additionally, the twist angle cannot be adjusted intentionally in the growth process, and the synthesis of the specific layer at a specific location is not controlled.
1：Experimental Design and Method Selection:
The study involved fabricating heterojunction devices with p-type WSe2 and n-type MoSe2 with different crystal orientation angles (0?, 15?, and 30?) to investigate the role of lattice matching in vertical heterostructures. High-resolution X-ray diffraction (HR-XRD) was used to estimate the crystal orientations of WSe2 and MoSe
2：Sample Selection and Data Sources:
Single crystal flakes of WSe2 and MoSe2 were obtained via micro-mechanical exfoliation using Scotch tape. The crystal orientation was determined using HR-XRD, and thin flakes were selected based on optical microscopy and atomic force microscopy (AFM) for smoothness and cleanliness.
3：List of Experimental Equipment and Materials:
Equipment included HR-XRD (PANalytical X'pert PRO), AFM (XE-100 by Park systems Inc., n-Tracer by Nano Focus Inc.), micro Raman systems (Nanofinder 30 and Renishaw, InVia systems), and e-beam lithography for electrode patterning. Materials included Scotch tape, polypropylene carbonate (PPC) film, chloroform, isopropanol, polymethyl methacrylate, Pd, Au, and Ti.
4：Experimental Procedures and Operational Workflow:
The process involved exfoliating flakes, determining crystal orientation, transferring flakes to a substrate, fabricating devices with specific twist angles, and characterizing the devices using PL, Raman spectroscopy, and electrical measurements under LED illumination.
5：Data Analysis Methods:
Data analysis included spectral responsivity and external quantum efficiency calculations, PL and Raman spectroscopy analysis, and I-V curve measurements under different LED illuminations.
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