Theoretical Study On Electronic Structure And Mobility Of Doped Gallium Nitride

Since the carrier mobility has an important impact on the photoconductivity characteristics of the device.The controllability of the material band gap can further affect on the carrier mobility,so that the material has a wider range of applications.In this paper,the electrical properties of materials are regulated by doping and external stress.The electronic structure and carrier mobility of Fe-doped GaN under uniaxial strain are studied by first-principles method.The details are as follows:Firstly,the electronic structures and effective mass of Ga15MgiN16 and Ga14MgiFeiN16 systems are studied,and the stability of the co-doped structures is analyzed from the formation energy and the phonon dispersion.The results show that the introduction of Fe increases the band density and deepens the impurity level.The influence of Mg doping on the magnetic properties of GaN-based diluted magnetic semiconductor(DMS)is also considered.The results show that the magnetic moment of Ga14MgiFe1N16 system is smaller than that of Ga15Fe1N16 system,which indicates that the doping concentration of Mg will hinder the binding of magnetic ions when it exceeds a certain threshold.We also found the difference of effective mass of Ga14MgiFe1N16 system in different directions is less than that of Ga₁₅Mg₁N₁₆ system,indicating that the anisotropy of the system was reduced by doping Fe.Secondly,by optimizing the Ga₃₁Fe₁N₃₂ system,the formation energy and phonon spectrum of the system under strain-free and uniaxial strain along x-axis are calculated to prove that the system exists stably in the studied strain range.The band gap calculated by generalized-gradient approximation(GGA)+U method and Heyd-Scuseria-Ernzerhof(HSE)06 method are compared,and the subsequent calculation of the paper is determined adopts HSE06 method.The band structure and optical properties of the system under uniaxial strain along x-axis are calculated.The results show that the symmetry of the system is changed by the strain in the range of±1.5%strain;Strain can regulate the band gap of the system,and gradually eliminate the degeneracy of heavy hole level and light hole level in valence band;The optical properties such as complex dielectric function and absorption coefficient under various strain conditions are also studied.It is found that the place where strain has a great influence on the optical properties of material is generally located at the point where the photon energy is zero.As a whole,the strained system has varying degrees of blue shift.In the low energy region,the peak value of all optical properties increase under tensile stress,while the peak value under compressive strain decreases to some extent.Finally,the effective mass,deformation potential and elastic constant of Ga31FeiN32 material are calculated by the above related data.It can be seen from the results that the material is a brittle material with great stiffness;Under the stress,the band edge energy at the conduction band minimum changes greatly,and the electron deformation potential is greater than the hole deformation potential.The effective mass of the electron is far less than the hole.The effective mass of electrons decreases with the change from compressive strain to tensile strain.Only the acoustic wave phonon scattering is considered in this paper,which makes the calculated carrier mobility larger and the upper limit of carrier mobility is presented.The calculated results accord with the intrinsic GaN experimental value trend that the electron mobility is much larger than the hole mobility.The variation trend of carrier mobility with effective mass of uniaxial strain along x-axis is obtained.