| Two-dimensional and monolayered materials have attracted increasing attention day by day and are considered as an alternative to traditional bulk semiconductors for future generation of nanodevices due to their novel structures and fancy electronic properties.Recently,a new type of two-dimensional materials,namely,phosphorene?black phosphorus sheet?has been successfully fabricated in the experiments.Owing to possesing a tunable band gap?0.3-1.5 eV?,a high surface-volume ratio,good carrier mobility(1000 cm2 V-11 s-1)and a high Ion/Ioffff ratio?105?,the black phosphoren holds great potential in applications of optoelectronic devices,field effect transistors and gas sensors.As we all know,the bare armchair phosphorene nanoribbon?APNR?is a semiconductor with an indirect band gap and lower carrier mobility;the bare zigzag phosphorene nanoribbon?ZPNR?is a metal.Therefore,it is necessary to understand the effect of electronic structure of phosphorene nanoribbons on the transport properties of matel-semiconductor junctions,TFET and gas sensors.In this paper,we have studied the electronic tunneling of phosphorene nanoribbons,and have discussed the influence of edge passivation and gas adsorption based on the first-principles:?1?Effects of edge passivation on rectifying performance of in-plane metal-semiconductor junctions of zigzag phosphorene nanoribbonsWe perform a systematic study of the band structures of passivated ZPNR and transport properties of in-plane metal-semiconductor junctions by combining density functional theory and the non-equilibrium Green's function.It is found that the ZPNR passivated by H,Cl or F atoms is semiconductor,and the ZPNR passivated by C,O or S atoms is metal.Accordingly,ZPNR with different passivated atoms are used to design an in-plane metal-semiconductor junction.The calculated current-voltage characteristics indicate that these in-plane metal-semiconductor junctions can show the excellent rectification behavior.More importantly,we find that the type of passivated atom plays a very important role in the rectification ratio of the in-plane metal-semiconductor junction.Our results are very useful for further design of functional nanodevices based on ZPNR.?2?Performance of tunneling field-effect transistor based on black phosphorus nanoribons through edge passivationWe investigate the band structures and transport properties of tunneling field effect transistor based on edge-passivated zigzag and armchair black phosphorus nanoribbons by using the first principles density functional thory.The results show that both ZPNR and APNR passivated by H,Cl or F atoms exhibit semiconducting characteristics;however,the effect of band gap regualation is inapparent.APNR TFET passivated by H,F and Cl with a gate length of 6.6 nm can achieve an on-state current up to 4×104 nA and a current swithing ratio of 105.ZPNR TFET passivated by H,F and Cl with a gate length of 6.6 nm can obtain a lower off-state current 10-88 nA,but a larger current swithing ratio of 109.?3?Selective adsorption of harmful molecules on zigzag phosphorene nanoribbon for sensing applicationsWe investigate the electronic structures and transport properties of hydrogenated zigzag phosphorene nanoribbon?ZPNR?after adsorption of four typical harmful molecules.The results show that SO3 and CCl4 both tend to be adsorbed on the top site of hydrogenated ZPNR.The NH3 and CH4 both tend to be adsorbed on a hollow site of hydrogenated ZPNR.Hydrogenated ZPNR exhibits a strong adsorption of SO3with the largest adsorption energy and charge transfer among four harmful molecules.Moreover,we also find that the adsorptions of CH3,CH4 and CCl4 have little effect on the band structure of hydrogenated ZPNR.However,the adsorption of SO3 can reduce the band gap obviously.The present work confirms that the hydrogenated ZPNR has strong selectivity of the absorbability.?4?High sensitivity and selectivity of hydrogenated ZPNR sensor in detecting SO3 gas moleculesThe sensing properties of hydrogenated ZPNR for SO3,SO2 and H2S gas molecules are theoretically investigated by the first-principle calculation based on density functional theory.The total energy,adsorption energy,and Mulliken charge transfer are calculated to evaluate the adsorption properties of the hydrogenated ZPNR for these gas molecules.The hydrogenated ZPNR shows the physical adsorption of all gas molecules.The results demonstrate that hydrogenated ZPNR is most sensitive to SO3 gas molecules with high adsorption energy and superior charge transfer.Furthermore,the adsorption of SO3 can modify the densities of states of hydrogenated ZPNR near the Fermi level.The current-voltage?I-V?curves reveal that the conductivity of the hydrogenated ZPNR is obviously increased after SO3adsorotion.Therefore,our results can provide a theoretical expectation for the potential applications of hydrogenated ZPNR in SO3 detecting. |
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