New Progress in Research of Two-dimensional Semiconductor Heterojunction

Recently, Kangjun, a doctoral student at the National Key Laboratory of Superlattice at the Institute of Semiconductors of the Chinese Academy of Sciences, and in the research team of Lijingbo, Lishushen, and Xiajianbai, he worked with Dr. Wanglinwang of the Lawrence Berkeley National Laboratory(LBNL). The research team has made new progress in the basic research of two-dimensional semiconductor Hetero junction. The relevant results were published on the NanoLetters hosted by the American Chemical Society on September 30.

Semiconductor Hetero junction is a structure formed by the contact of different semiconductor materials. Since the two semiconductor materials that make up the Hetero junction have different physical parameters such as bandgap width, electron affinity energy, dielectric constant, and absorption coefficient, the Hetero junction will exhibit many properties that are different from those of a single half conductor material. In the traditional semiconductor field, electronic devices made with semiconductor Hetero junction as the core, such as photodetectors, light-emitting diodes, solar cells, lasers, etc., often have superior performance than similar devices made of single half conductor materials.

In recent years, a new type of two-dimensional semiconductor material represented by two-dimensional Molybdenum disulfide(MoS2) and Molybdenum selenide(MoSe2) has rapidly become the research frontier in the field of materials science. The thickness of such semiconductors is only a few atoms, and it is expected to become a two-dimensional platform for a new generation of electronic devices. The accumulation of different two-dimensional semiconductor layers forms a two-dimensional semiconductor Hetero junction, and the novel physical phenomena in such Hetero junction have also become a focus of international nanotechnology research.

In this context, the research team of Semiconductor and LBNL applied the first principle to calculate the structure and electronic properties of the two-dimensional MoS2/MoSe2 Hetero junction. The two-dimensional MoS2 and MoSe2 monolayers have 4.4 % lattice mismatches. Through the calculation of strain energy and binding energy, it was found that the strength of Fandewaersi's binding effect between them was not enough to eliminate this mismatch to form a Hetero junction of lattice matching, but to form a structure called Moiré Patters.

In the Mohs pattern, the accumulation methods of MoS2 and MoSe2 in different regions are also different, resulting in different interlayer coupling effects and different electrostatic potentials in different regions, which will have a significant impact on the electronic structure of Hetero junction. In order to further explore the regulatory effect of Mohs pattern on Hetero junction electronic structure, a new linear scaling algorithm was used to calculate the edge wave function of a MoS2/MoSe2 Mos pattern Supercell containing 6630 atoms. The results show that the cavitation wave function at the top of the valence band is limited to the area with strong interlayer coupling, while the electron wave function at the bottom of the conduction band is relatively extended, showing only weak locality. The results indicate that the formation of the Mohs pattern and the resulting localization of the wave function will be the universal properties of the two-dimensional semiconductor Hetero junction. These new findings will provide theoretical guidance for the preparation of two-dimensional semiconductor Hetero junction devices.

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

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