| The related theoretical researches indicate that the transition-metal dichalcogenides from group IVB exhibit higher carrier mobility than group VIB.Moreover,the Zr S2of group IVB disulfides has the best stability and excellent visible light response,which make it have great potential in the field of optoelectronic devices.In this thesis,two kinds of Zr S2based van der Waals heterostructures are constructed.The effects of twist,stress and electric field on the electronic structure and optical properties for the two heterostructures are studied by using the first-principles based on the density functional theory.The specific researches are as follows:The H-Zr S2/Hf S2van der Waals heterojunction conststed of H-Zr S2and H-Hf S2can be significantly improved the absorption coefficient located at the visible region.However,the indirect band gap of H-Zr S2/Hf S2limits its application in the field of optoelectronic technology.By applying the certained twist angle?13.2°,17.9°,42.1°and 46.8°?or a uniaxial compression stress of-6%?-11%in the x direction,the H-Zr S2/Hf S2heterostructure can be modulated into the direct band gap.Therefore,the H-Zr S2/Hf S2can be used as luminescent materials.Simultaneously,the twist angle and uniaxial compression stress in the x direction makes the optical anisotropy of heterojunction more significant.The absorption coefficient of the heterostructure under the?001?and?100?direction located at the visible region can be obviously improved by applying the twist angle.The uniaxial compression stress of-6%?-11%in the x direction can strengthen the absorption coefficient in the?001?direction and absorption coefficient in the?100?direction reduces because the absorption peak moves to the infrared region.The band gap of H-Zr S2/Hf S2can be modulated by applying electric field,nevertheless,the indirect band gap of heterojunction cannot be modulated into the direct band gap.The T-Zr S2/h BN van der Waals heterojunction possesses a direct gap,and both the conduction band minimum and valence band maximum locate at the?point in the Brillouin zone.The results indicate that the T-Zr S2/h BN under the determined twist angle,excessive tensile or compression stress can be modulated to indirect gap,which is not conducive to the applications in the optical devices region.In addition,applying electric field can linearly modulate the band gap of T-Zr S2/h BN heterostructure without changing the direct band gap.Compared with the T-Zr S2monolayer,the absorption coefficient of T-Zr S2/h BN located at the visible region is not significantly improved.Only applying the angle of 60°,biaxial compressive stress of?xy=-1%?-6%,uniaxial compressive stresss in x direction of?xx=-1%?-4%,uniaxial compressive stresss in y direction of?yy=-1%?-4%or negative electric field to the T-Zr S2/h BN heterojunction,the absorption coefficient located at the visible region in the?001?direction can be remarkably improved. |
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