Study On Tuning Electronic Structure Of Monolayer Phosphide Semiconductors And Their Interfaces With Metal

In order to develop multi-functional and high-performance devices with the demand of various semiconductor materials,and break the bottleneck of contact barriers between semiconductor materials and metal electrode,the monolayer calcium phosphide and indium triphosphide with a high electron mobility have been a good candidate and are now a rapidly expanding research.The first-principles calculation method based on density functional theory（DFT）is used to study the electronic structure,magnetics and optics characteristics of calcium triphosphide such as substitution and vacancy doping and the introduction of buffer layers,and to investigate the contact characteristics of the interface between indium triphosphide and nickel.The theoretical results play a vital importance of designing multi-functional semiconductor devices.The main research results are divided into two parts:1. Tuning electronic,magnetic and optical properties of monolayer calcium triphosphate（m-CaP₃）through substitution and vacancy dopings.This work primarily-includes three parts:（1）Based on substituting doping or introducing vacancies for two types of P atoms and Ca of 2×2 supercells of m-CaP₃,we calculated the total energy,formation energy and electron transfer of each system to obtain the most stable unit cell structure of each doped system,The effects of doping element types（B,C,N,O,and F）on the band gap and spin polarization characteristics of m-CaP₃ were studied.（2）The above defects were further introduced into the 1×1,3×3 and 4×4supercells of m-CaP₃,and the effects of the defect concentration on the electronic structure,especially on the band gap and spin polarization characteristics of each doping system were analyzed.（3）The effects of doping concentration on optical absorption character of m-CaP₃were explored.Through the above research,it was found that changing the doping element and doping concentration of m-CaP₃ not only realize the tunability of the band gap in different energy ranges,but also keeps the good optical absorption characteristics in the entire visible light range.2. Synergistically tuning the interface contact characteristics of the monolayerindium triphosphide（m-In P₃）and metal nickel（Ni）heterostructure by inserting buffer layer.This work is mainly divided into three parts:（1）We investigated the equilibrium layer spacing and the electronic characteristics of the contact interface of the heterostructures formed by m-In P₃ with G,m-BN and Ni,and analyzed the reasons why the contact characteristics violate the Schottky-Mott rule.（2）By introducing graphene or m-BN buffer layer at the contact interface of the electrode,we calculated and explored the effect of the buffer layer on the Fermi pinning at the contact interface and the energy band alignment of the interface.（3）For the systems with buffer layer,we theoretically studied the effect of vacancy defects on the electronic characteristics of the contact interface of m-In P₃.Through the above three aspects of research,we can effectively remove the Fermi pinning and tune the energy band alignment at the interface by introducing m-In P₃vacancy defects and graphene or m-BN buffer layers at the m-In P₃@G and m-In P₃@Ni heterogeneous interfaces,which results in the contact characteristics changes from Schottky contacts to ohmic ones.This paper provides an important theoretical basis for the electronic,optoelectronic and energy conversion devices application of two-dimensional metal phosphides in the future.