Strain-tunable Electronic And Optical Properties Of Two-dimensional Semiconductor HfX₂?C₃N?GeP And Green Phosphorene

As a vital nanomaterial,the research of two-dimensional semiconductor materials is a hot research topic.The electronic and optical properties of 2D semiconductor materials are closely related to the crystal structure,the electronic structure,and the environment.Thus,the study of the effects of different modifications and regulation methods on the properties of 2D semiconductor materials is an important research direction.Notably,strain engineering is an effective tunable approach to alter the electronic and optical properties of 2D semiconductor materials.Therefore,the study of the electronic and optical properties of 2D semiconductor materials tuned by strain is of great significance.It is not only helpful to explore the novel properties of 2D materials but also beneficial to improve its performance in practical application and expand its application range.With the development of related theories,the first-principle calculation based on DFT theory,as a research method widely used in physics,chemistry,and other disciplines in recent years,can efficiently explore the physical properties and chemical properties of materials.In this paper,we systemically studied the structural properties,electronic properties and optical properties of some new two-dimensional(2D)materials under the influence of the in-layer strain.Some main conclusions are as follows:1.We characterized the structural stability,electronic and optical properties of novel two-dimensional(2D)monolayer transition-metal dichalcogenide(TMDs)Hf X₂(X=S,Se).It is indicated that monolayer 1-T Hf S₂and Hf Se₂present a stable indirect band gap semiconductor when the strain is 0%.The band gap of all monolayer 1-T Hf X₂decreases significantly and the optical absorption edge shows an obvious red-shift trend with an increasing in-layer biaxial compressive strain.When the compressive strain is greater than-8%in Hf S₂and-6%in Hf Se₂respectively,the band gap decreases to zero,and so the semiconductor-metal transition was produced.Conversely,the band gap increases insignificantly with the increasing in-layer biaxial tensile strain from 0%to+10%while the absorption edge reveals an inconspicuous blue-shift trend.Moreover,with the vertical electric field(E-field)increases,there is the band gap decreases and the absorption edge red shifts in all monolayer Hf X₂under different in-layer biaxial strains.Our study suggests that the strain and electric field(E-field)engineering are effective tunable approaches to alter the electronic and optical properties of monolayer Hf X₂.2.The optical properties,structural properties and electronic properties of a new two-dimensional(2D)monolayer C₃N under different strains are studied in this paper.It is a stable indirect band gap 2D semiconductor when the strain is 0%.It could maintain indirect semiconductive characters under different biaxial and uniaxial strain from?=-10%to?=10%.As for its optical property,when the uniaxial strain is applied,the absorption and reflectivity along armchair and zigzag directions exhibit an anisotropy property.However,an isotropic property is presented when the biaxial strain is applied.Most importantly,both uniaxial tensile strain and biaxial tensile strain could cause the high absorption coefficient of monolayer C₃N in a deep ultraviolet region.This study implies that strain engineering is an effective approach to alter the electronic and optical properties of monolayer C₃N.3.This paper studies the structural,electronic and optical properties of the new group IV-V two-dimensional(2D)material Ge P with changes in strain.The results show that monolayer Ge P is a 2D semiconductor with highly dynamically stable as well as low structural symmetry.In terms of the electronic property,it remains semiconductivity in the range of-10%compressive strain to 10%tensile strain.As for the optical property,it is anisotropic.When Ge P is subjected to strain,regardless of the direction of the strain,the optical property of monolayer Ge P is significantly affected more by tensile strain than by compressive strain.In particular,the monolayer Ge P is most susceptible to deformation by strain in a direction,and only compressive strain in a direction will cause Ge P to undergo a transition from an indirect band-gap semiconductor to a direct band-gap semiconductor,which results in the improvements of absorption efficiency and reflectivity efficiency in the low energy regions.4.The effect of in-layer strain on the optical and electrical properties of monolayer green phosphorene,a new anisotropic two-dimensional(2D)material,has been systematically studied.Green phosphorene can be viewed as a combination of black and blue phosphorene segments in regular order.The results reveal that,firstly,strain-free monolayer green phosphorene is a stable direct band-gap 2D semiconductor with the anisotropic optical property.Secondly,the optical properties,such as the absorption coefficient and reflectivity,along armchair and zigzag direction respond very differently to the various applied strains.As for the electronic properties,the band gap exhibits different changing trends by applying either in-layer biaxial strain or uniaxial strain in different directions.By calculating and comparing the energies of near-band-edge states after applying different strains on green phosphorene,the reason for the anisotropy of the new 2D material is analyzed.This study implies that green phosphorene can be used in linear polarizers and other anisotropic photoelectric devices.In short,2D materials are suitable for nanoelectronic and optoelectronic applications in the future.It is of great significance to systematically study the strain tunable electronic and optical properties of 2D materials.