石墨烯/MoS_(2)异质结的界面相互作用及其肖特基调控的理论研究

Theoretical study on interface interaction and Schottky regulation of graphene/MoS_(2)heterojunction

本文基于第一性原理方法,系统研究了外电场对石墨烯/MoS2范德瓦耳斯异质结界面相互作用及其电子性质的影响.计算结果表明石墨烯和MoS2之间通过微弱的范德瓦耳斯力结合形成异质结,石墨烯/MoS2异质结的能带基本上是单层石墨烯和单层MoS_(2)能带结构的简单叠加并形成了N型肖特基势垒;由于异质结的石墨烯层的电子向MoS_(2)层转移,导致石墨烯表面带正电,MoS_(2)表面带负电,在异质结内部形成了方向由石墨烯指向MoS2的内建电场.此外,对异质结施加不同强度的负电场时,体系的接触类型逐渐由N型肖特基接触类型转变为欧姆接触;对异质结施加不同强度的正电场时,体系的P型肖特基势垒呈降低趋势,体系的N型肖特基势垒呈现先缓慢升高再急剧下降的特点,在电场强度提高至5.0 V·nm^(-1)附近时,接触类型由N型肖特基接触转变为P型肖特基接触.此项工作将对相关二维场效应晶体管的设计提供参考.

In practical metal-semiconductor contact applications,the existence of Schottky barrier seriously reduces the performance of the device.Therefore,it is important to obtain a smaller Schottky barrier or even ohmic contact.Based on the first-principles method,this paper systematically studies the effect of external electric field on the interface interaction and electronic properties of graphene/MoS_(2)van der Waals heterostructure.The calculation results show that graphene and MoS_(2)combine to form a heterojunction through a weak van der Waals force,and the energy band of graphene/MoS_(2)heterojunction is basically a simple superposition of the energy band structure of single-layer graphene and single-layer MoS_(2),forming an N-type Schottky barrier.Due to the transfer of electrons from the graphene layer of the heterojunction to the MoS_(2)layer,the graphene surface has a positive charge and the MoS_(2)surface has a negative charge,and an internal electric field with the direction from graphene to MoS_(2)is formed in the heterojunction.In addition,when the negative electric field of different strength is applied to the heterojunction,the contact type of the system gradually changes from N-type Schottky contact type to ohmic contact type.When a positive electric field of different intensities is applied to the heterojunction,the P-type Schottky barrier of the system decreases,and the N-type Schottky barrier of the system shows a slow rise and then a sharp decline.When the electric field intensity increases to 5.0 V·nm^(-1),the contact type changes from N-type Schottky contact to P-type Schottky contact.In order to further explore the change of Schottky barrier between 5.0~6.0 V·nm^(-1),the change curve of the Schottky barrier height of the system under different electric field intensities with the step of 0.2 V·nm^(-1)is calculated and described.The results show that when the electric field intensity increases from 5.0 to 5.8 V·nm^(-1),the contact type of the system presents gradually P-type Schottky contact,and when the electric field intensity increases to 6.0 V·nm^(-1),the contact type of the system changes from P-type Schottky contact type to ohmic contact.To sum up,applying an external electric field has a great influence on the graphene/MoS_(2)heterojunction system.It can not only realize the transformation of its Schottky contact type from N-type to P-type,and then from Schottky contact to ohmic contact,but also effectively control its Schottky barrier height.This work will provide a reference for the design of related two-dimensional field effect transistors.