Ab Initio Study Of The Structural Stability And Electronic Structure Of Damaged Ga_xAl_1-xAs/GaAs Semiconductor Superlattice

Semiconductor superlattice materials have many new physical properties due to their special structures,such as negative resistance effect and quantum hall effect.Because of its unique physical properties,it is widely used in weapons and space-based fields.In the applications,semiconductor superlattice materials are exposed in fluxes of neutrons and gamma rays,which result in defect generation and aggregation,and ultimately deteriorate the electric properties.How to enhance the electrical properties and radiation tolerance of electronic materials is thus critical to ensure that electronic devices work properly and efficiently in a radiation environment.In this paper,by comparing the electronic structures of ideal and defective GaAlAs/GaAs semiconductor superlattices,we determine the influence of the changes in the internal structure of GaAlAs/GaAs semiconductor superlattices on their electrical properties.The results of this paper will be helpful to improve the electrical and radiation resistance of electronic materials.It can provide theoretical support for the research and development of new electronic materials,and is of significant importance for scientific research and engineering application.First,we investigate the electronic structure of the bulk phase ternary mixture GaAlAs and the GaAlAs/GaAs semiconductor superlattice with different stacking periodicity using density functional theory.The geometric structures of GaAlAs/GaAs superlattices with different stacking periodicity,i.e.,(Ga_xAl_1-xAs)_n/?GaAs?_m?m,n=1-5,x=0.25,0.5 and 0.75?,are optimized,and their electronic structures and carrier transport properties are calculated.The results show that when the number of layers of GaAs and GaAlAs in the superlattice is fixed,the band gap width of(Ga_xAl_1-xAs)_n/?GaAs?_m semiconductor superlattice decreases with the increasing concentration of Ga component.When the content of Ga component is fixed,the band gap width of semiconductor superlattices decreases with the increase of GaAs layers and increases with the increase of GaAlAs layers.Besides,we find that there are certain relationship between electron mobility of semiconductor superlattice and Ga composition concentration as well as stacking periodicity.When the layers of GaAs and GaAlAs are fixed in the superlattice,the electron mobility increases with the increasing content of Ga composition.For a given concentration for Ga component,the electron mobility increases with the increase of GaAs layers and decreases with the increase of GaAlAs layers.It is found that the(Ga_0.75Al_0.25As)₁/?GaAs?₅ semiconductor superlattice has the minimum electron effective mass of 0.033m_e and the maximum mobility of 2.134×10⁴cm²/Vs.These results show that the band gap width and carrier mobility can be tuned by controlling the number of layers and component concentration of superlattices,which will provide theoretical support for the fabrication of high-performance electronic devices.Subsequently,the stability of various point defects,which include X vacancy?V_X,X=Ga,Al and As?,X interstitial(X_int),X occupying the As lattice site(X_As)and As occupying the X lattice site?As _X?in the Ga_0.5Al_0.5As/GaAs semiconductor superlattice is studied.The defect formation energies of various defects are calculated and the effect of point defects on the electronic structure and transport properties of Ga_0.5Al_0.5As/GaAs semiconductor superlattices are explored.The results show that the interstitial and vacancy defects are always difficult to form under both As-rich and Ga-rich chemical environments.Under the As-rich condition,the two antisite defects of As_Ga and As _Al are easier to form,while under the Cation-rich condition,the two antisite defects of Ga_As and Al _As are easier to form.It is also noted that the antisite defects affect the geometric structure of superlattices slightly,while the band gap is narrowed and even metallicity is induced.Consequently,the electron mobility is improved by the presence of antisite defects.This is different from vacancy defects,which decrease the electron mobility significantly.These results indicate that the conductivity and irradiation resistance of electronic devices can be improved by proper intervention of defect generation,which will be of great significance for the application of semiconductor materials in irradiation environment.