Recently, Kang Jun, a doctoral student of the State Key Laboratory of Superlattices at the Institute of Semiconductors, Chinese Academy of Sciences, worked with Dr. Li Jingbo, academician Li Shushen, and academician Xia Jianbai to collaborate with Dr. Wang Linwang of the Lawrence Berkeley National Laboratory (LBNL) in the two-dimensional semiconductor industry. New progress has been made in the basic research of heterojunctions. The related results were published on September 30 in the Nano Letters organized by the American Chemical Society.

A semiconductor heterojunction is a structure formed by the contact of different semiconductor materials. Since the two semiconductor materials that make up the heterojunction possess different physical parameters such as band gap, electron affinity, dielectric constant, absorption coefficient, and the like, the heterojunction will exhibit many properties different from a single semiconductor material.

In the field of traditional semiconductors, electronic devices fabricated with semiconductor heterojunctions as cores, such as photodetectors, light emitting diodes, solar cells, and lasers, often have superior performance 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 frontiers in the field of materials science. The thickness of these semiconductors is only a few atoms, and is expected to become a two-dimensional platform for a new generation of electronic devices. Stacking different two-dimensional semiconductor layers forms a two-dimensional semiconductor heterojunction, and novel physical phenomena in such heterojunctions have also become a focus of current international nanoscience research.

In this context, the semiconductor group and LBNL's research team 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. From the calculation of the corresponding energy and binding energy, it was found that the strength of Van der Waals bonding between them was not sufficient to eliminate this mismatch and form a lattice-matched heterojunction, but formed a pattern known as the Mohs pattern ( Structure of Moiré Pattern).

In the Mohs pattern, the stacking modes of MoS2 and MoSe2 in different regions are also different, which in turn leads to different interlayer coupling and electrostatic potentials in different regions, which will have a significant effect on the electronic structure of the heterojunction. In order to further explore the role of Mohs pattern in the regulation of the electronic structure of heterojunctions, the team used a new linear scaling algorithm to calculate the band-edge function of a MoS2/MoSe2 MoS2-like 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, while the electron wave function at the bottom of the conduction band is relatively extended, showing only weak locality. The results of the study indicate that the formation of the Mohs pattern and the resulting localization of the wave function will be the universal nature of the two-dimensional semiconductor heterojunction. These new findings will provide theoretical guidance for the preparation of two-dimensional semiconductor heterojunction devices.

This work was supported by the "973" project of the National Outstanding Youth Fund and the Ministry of Science and Technology.

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