Electronic Structures And Transport Properties Of Two-Dimensional Phosphorene

In recent decades,the development trend of semiconductor chip integration and miniaturation has greatly promoted the advance of information technology industry.Every upgrade of electronic information system and every change and innovation of semiconductor technology will make higher requirements on performance of electronic semiconductor chips.However,the size of the transistor in the chip becomes a hindrance to its development,and there are two main problems that need to be solved:(1)electrostatic control problem:when the transistor channel is short,the control ability of the grid to the channel area is poor;(2)power consumption problem:when the size of the transistor becomes smaller and the device structure becomes thinner,the leakage current and power consumption will increase,which will also bring about heat dissipation problem.In order to solve the problems of these two aspects,we can find these two ways:(1)searching for new material system,and(2)exploring new ways to reduce the working voltage.At this time,the appearance of two-dimensional(2D)materials has greatly improved the performance of various aspects of electronic devices.In this project,my research focuses on the electronic properties of 2D material,black phosphorus,and transport properties of the electronic devices based on layered phosphorus.On one hand,we study electronic structures and properties of heterostructures based on four layered phosphorus of different phases,namely ?-P,?-P,?-P and ?-P.On the other hand,we build tunneling field effect transistors(TFET)based on layered phosphorus and research the transport properties by analyzing the negative differential resistance(NDR)effect,on/off current ratio and subthreshold swing(SS)of TFET.The combination of 2D materials by layer-by-layer stacking into vertical heterostructures has been identified as a new promising way to improve or enrich the functionalities of these materials.We build six van der Waals(vdW)heterostructures by stacking the four different types of layered allotropes of phosphorus.Each heterostructure contains two different phases.We investigate the structural and electronic properties of heterostructures based on the first-principles calculations.The strength of the interaction between the two layers is studied by checking differential charge density and electronic localized function in the heterostructures,suggesting a weak vdW interaction between these two layers.The relationship between the energy evolution and movements in the armchair(x)and zigzag(y)directions of all these vdW heterostructures was investigated.We discover a common character that the most stable heterostructure is the one that shows the fewest overlap between the atoms of the two layers.Then we calculate band structures and research band alignments of the six heterostructures.All these structures are semiconductors,with band gaps ranging from 0.25 eV to 0.69 eV.Band alignments contain type-? and type-?.By appropriately adjusting the doping concentration,the band alignment of heterostructures can be changed from type ? to type ?.The multiple types of band alignment suggest high potential of the phase manipulated 2D phosphorus for the next-generation novel electronics.Metal oxide semiconductor field effect transistor(MOSFET)usually has high power consumption due to its working principle.Instead of thermionic emission as in the case of MOSFET,TFET is based on the switching mechanism of band to band tunneling.Hence,TFET does not suffer from the 60 mV/dec SS limit,providing a new prospect for low power applications.In this paper,we investigate transport properties of the p-i-n TFETs based on in-plane and vertical heterostructures composed of semi-infinite ?-P and ?-P layers.Then we apply appropriate bias voltage,and investigate the relationship between NDR effect and intrinsic region length by analyzing transmission spectra and device local density of states.We discover that both the in-plane and vertical ?-? tunneling junctions show significant NDR effect and different integration of heterostructures can affect the NDR effect.Due to the poor gate control and serious short channel effects with the short channel of 5 nm,we build a long channel TFET to further research transport characteristics of TFET.Finally,we find vertical TFET has better performances in NDR effect,on/off current ratio and SS than in-plane TFET composed of ?-P and ?-P,which is resulting from the distinct interaction nature of the ?-P and ?-P layers in the heterostructures.