Recently, Dr. Kang Jun, Ph.D. student of the State Key Laboratory of Superlattice, Institute of Semiconductors, Chinese Academy of Sciences, in the research team of Li Jingbo, Academician Li Shushen and Academician Xia Jianbai, cooperated with Dr. Wang Linwang, Research Group of Lawrence Berkeley National Laboratory (LBNL), in 2D Semiconductor New progress has been made in basic research on heterojunctions. The results were published on the NanoLetters hosted by the American Chemical Society on September 30, 2013.
Semiconductor heterojunctions are structures formed by the contact of different semiconductor materials. Since the two semiconductor materials constituting the heterojunction possess different physical parameters such as forbidden band width, electron affinity, dielectric constant, and absorption coefficient, the heterojunction will exhibit many properties different from a single semiconductor material. In the traditional semiconductor field, electronic devices fabricated with semiconductor heterojunctions, such as photodetectors, light-emitting diodes, solar cells, and lasers, often have superior performance compared to similar devices fabricated from a single semiconductor material. In recent years, new two-dimensional semiconductor materials represented by two-dimensional molybdenum disulfide (MoS2) and molybdenum diselenide (MoSe2) have rapidly become the research front in the field of materials science. These semiconductors are only a few atoms thick and are expected to be the two-dimensional platform for next-generation electronic devices. Two-dimensional semiconductor heterojunctions are formed by stacking different two-dimensional semiconductor layers, and the novel physical phenomena in such heterojunctions have become a focus of international nanoscience research.
In this context, the semiconductor and LBNL research groups applied first-principles calculations to study the structural and electronic properties of two-dimensional MoS2/MoSe2 heterojunctions. There is a 4.4% lattice mismatch in the two-dimensional MoS2 and MoSe2 monolayers. Through the calculation of the corresponding energy and binding energy, it is found that the strength of van der Waals bonding between them is not enough to eliminate this mismatch to form a lattice-matched heterojunction, but to form a pattern called Mohs ( The structure of MoiréPattern). In the Mohs pattern, the accumulation patterns of MoS2 and MoSe2 in different regions are also different, which leads to different interlayer coupling and electrostatic potential in different regions, which will have a significant impact on the electronic structure of the heterojunction. In order to further explore the regulation of the Mohs pattern on the electronic structure of the heterojunction, the research team used a new linear scale algorithm to calculate the band-edge function of a MoS2/MoSe2 Mohs pattern supercell containing 6630 atoms. . The results show that the hole wave function at the top of the valence band is limited to the region where the interlayer coupling is strong, and the electron wave function at the bottom of the conduction band is expanded, showing only weak locality. The results suggest that the formation of the Mohs pattern and the resulting localization of the wave function will be the general nature of two-dimensional semiconductor heterojunctions. These new discoveries will provide theoretical guidance for the preparation of two-dimensional semiconductor heterojunction devices.
The work was supported by the National Outstanding Youth Fund and the 973 Program of the Ministry of Science and Technology.
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