First-Principles Study On The Optoelectronic Properties Of CdO/MoS₂, GaS/GeSe And HfSSe/BSe Heterostructures

In recent years,two-dimensional（2D）materials,represented by graphene,have leaped to the forefront of scientific research on semiconductor materials due to their excellent physical and electronic properties.The inherent shortcomings of single 2D semiconductor materials cannot meet the needs of modern information industry applications,so it is essential to develop new multifunctional semiconductor materials.The vertical stacking of two materials to form a heterostructure with a unique interface state is the optimal solution to this challenge and is gaining momentum.Heterostructures also provide a common design platform and direction for developing high-performance semiconductor materials and devices.In this paper,2D CdO/MoS₂,GaS/GeSe and HfSSe/BSe van der Waals heterostructures are investigated.First-principles calculations can systematically describe geometrical configuration to optoelectronic properties and explore their variation under external modulation.The results are expected to provide new ideas for the experimental preparation of novel heterostructure devices.The contents are as follows:Construction of novel CdO/MoS₂ van der Waals heterostructure based on the suitability of CdO and MoS₂ monolayers.The results show that the CdO/MoS₂ heterostructure forms a built-in electric field at the interface from MoS₂ towards CdO.In combination with its inherent Type-II indirect band gap electronic structure further confines the photogenerated electrons and holes to different spaces.Bader charge analysis indicates that there are 0.060|e|involved in formation of the interfacial state.Compared to the two monolayers,the band edge position of the heterostructure encapsulates the redox potential of water.It has excellent light absorption properties(～5.32×10⁵ cm^-1)for the photolytic water reactions.In addition,biaxial strain can significantly reduce the band gap of the CdO/MoS₂ heterostructure,but the system still maintains the original Type-II indirect electronic structure.Notably,tensile strain can effectively reduce the effective mass（0.34 m₀）of electrons in the heterostructure and further increase the absorption intensity in the visible region.The above results provide theoretical guidance for designing and fabricating of CdO/MoS₂ heterostructure optoelectronic devices.The GaS/GeSe heterostructure with three stacked configurations are constructed vertically from GaS and GeSe nanospheres,and the most stable structure is used as the target for an in-depth study of the optoelectronic properties.The results show that the intrinsic energy band interleaving structure of GaS/GeSe heterostructure together with the built-in electric field overcome the Coulomb forces between electron holes and place the photogenerated carriers in different spaces.The band alignment potential of the heterostructure crosses the redox potential of the water decomposition,meaning that the redox reactions of water proceed smoothly.Furthermore,at 2%compressive strain,the GaS/GeSe heterostructure undergoes a band structural transition and improves its band alignment potential as well as visible light absorption properties in an acidic environment.At 11%compressive strain,the heterostructure undergoes a semiconductor-metal transition.These novel properties suggest that GaS/GeSe heterostructure could be promising new materials for microelectronic devices.Single-layer HfSSe and BSe are vertically stacked to form a heterostructure with interleaved energy bands and a built-in electric field.Analysis of the work function and charge transfer reveals that the photogenerated carriers will move along a Z-scheme path.When a vertical electric field is applied,the HfSSe/BSe heterostructure triggers a semiconductor-metal transition due to the avalanche multiplication effect.The transition of the system from Type-II to Type-I occurs in the negative electric field range from 0 V/（?）increasing to-0.2 V/（?）.In addition,biaxial versus uniaxial compressive strains of 4%lead to an abrupt closure of the HfSSe/BSe heterostructure band gap.A 1%uniaxial tensile strain induces a transition from a direct to an indirect band gap in the HfSSe/BSe heterostructure.In summary,such stable HfSSe/BSe heterostructure are expected to be developed for applications in microelectronic devices such as transistors.