Phosphorene Can Control The Band Gap And Optical Properties

Due to the size-restricted effect,two-dimensional?2D?materials exhibit many excellent properties in electrical,optical and mechanical properties that are different from traditional three-dimensional crystal materials,and have broad application prospects in the fields of transistors,sensors,energy storage and other areas.Graphene and two-dimensional transition metal dichalcogenides?TDMs?are two kinds of two-dimensional materials which have been studied most widely.Graphene has extremely high electron mobility and excellent conductivity,but the lack of band gap limits its application in electronic devices.By contrast,TDMs have good thermal stability and chemical stability,but the mobility is relatively low,which is limited in practical applications.As a new type of two-dimensional direct bandgap semiconductor material,black phosphorus?BP?has excellent electrical and optoelectronic properties because of its low-dimensional effect.It combines the advantages of graphene and TDMs,and has high carrier mobility and switching ratio,which has aroused the attention of researchers.The band gap of black phosphorus is a direct band gap,which belongs to a bipolar narrow band gap semiconductor,and the type of band gap does not change with the change of black phosphorus thickness.The carrier mobility of the black phosphorus FET device can reach 10000 cm²V^-1s^-1,which is slightly lower than the carrier mobility of graphene but much higher than the transition metal sulfide.In addition,due to the anisotropy of the black phosphorus crystal structure,the band gap of the black phosphorus can be regulated within a wide range under the action of the external field,so the black phosphorus has a huge potential application in the field of flexible optoelectronic devices.In this paper,based on the first-principles method density functional theory,the electronic structure and optical properties of two-dimensional black phosphorus were calculated.In addition,the effect of biaxial strain?from 12%compressive strain to 12%tensile strain?on the band structure of a single layer of black phosphorus crystals has also been investigated.The study found that the application of external stress can be a moderate and effective adjustment of its band gap in the range of 0 to 1.845 eV.The compressive strain can lead to a single layer of black phosphorus transforming the metal properties from the semiconductor,while the stretching only affects the bandgap size of the system,but the applied stress does not change the direct bandgap characteristics of the black phosphorus.Based on the electronic properties of a single layer of black phosphorus,the optical properties of this material were analyzed in detail and the effects of strain on the optical properties were systematically discussed.It is found that the system exhibits significant optical anisotropy along different directions,and the external stress has a great influence on the optical properties of the system.Therefore,the application of external stress is an effective means of adjusting the bandgap and optical properties of the monolayer of black phosphorus.Black phosphorus nanotubes have potential in the field of optoelectronics due to their low-dimensional effects.In this work,the bending strain energy,electronic structure,and optical properties of black phosphorus nanotubes were investigated by using the first-principles method based on density functional theory.The results show that these properties are closely related to the rolling direction and radius of the black phosphorus nanotube.All the calculated black phosphorus nanotube properties show direct bandgaps,and the black phosphorus nanotubes with the same rolling direction express a monotone increasing trend in the value of bandgap with a decrease in radius,which is a stacking effect of the compression strain on the inner atoms and the tension strain on the outer atoms.The bending strain energy of the zigzag phosphorene nanotubes?zPNTs?is higher than that of armchair phosphorene nanotubes?aPNTs?with the same radius of curvature due to the anisotropy of the black phosphorus's structure.The imaginary part of the dielectric function,the absorption range,reflectivity,and the imaginary part of the refractive index of aPNTs have a wider range than those of zPNTs,with higher values overall.As a result,tunable black phosphorus nanotubes are suitable for optoelectronic devices,such as lasers and diodes,which function in the infrared and ultra-violet regions,and for solar cells and photocatalysis.In chapter 5,three new phosphenes??-P,?-P,and?-P?were systematically studied using the first-principles method.They had a honeycomb-like fold structure similar to that of black phosphorus??-P?.The electronic structures and optical properties of four novel phosphenes??-P,?-P,?-P and?-P?were studied.The results show that?-P and?-P are semiconductors with direct bandgap of 1.509 eV and 0.973 eV,and?-P and?-P are semiconductors with indirect bandgap of 1.874 eV and 1.772 eV.All of them exhibit strong UV absorption and UV reflection,and can be used as UV detection equipment or UV protection materials.The energy loss is concentrated in the UV region and has good light storage performance.