First-principle Calculations Of Electronic And Optical Properties Of ?-Ga₂O₃ With Oxygen Vacancies And Ti,Al Doping

?-Ga₂O₃ is a new kind of ultra-wide band gap semiconductor material,which has excellent characteristics such as ultra-wide band gap?4.9 e V?,high theoretical breakdown electric field?8 MV/cm?and high Baliga's figure of merit.As the next generation of high-power device material,?-Ga₂O₃ has attracted more and more attention.In addition,?-Ga₂O₃ has a broad application prospect in the fields of ultraviolet detector and gas sensor.At present,the intrinsic defects in the process of material preparation will have an important impact on the properties of the material,and the oxygen vacancy,as a common defect structure in?-Ga₂O₃ material,will be studied in this paper.In addition,doping,as a key problem affecting the properties of materials,is regarded as the research difficulty and breakthrough point of?-Ga₂O₃materials.Therefore,titanium?Ti?and aluminum?Al?are selected as doping elements to study the effect of metal doping on?-Ga₂O₃.The main research contents and results of this article are as follows:?1?Based on the density functional theory,the crystal structure,electronic structure and optical properties of?-Ga₂O₃ with different oxygen vacancy concentration?1.25 at%,1.67 at%and 2.50 at%?are calculated.Under the calculation of GGA+U method,the intrinsic?-Ga₂O₃ lattice parameters and photoelectric properties agree with the experimental values.When there is oxygen vacancy in?-Ga₂O₃,the bond length and bond angle in?-Ga₂O₃ change,and the oxygen vacancy in O2 position causes the largest lattice distortion and the largest decrease in structure volume.Among the three oxygen vacancy positions,the formation energy of O1 is the lowest.However,the formation energy of oxygen vacancy will be lower under the condition of poor or low concentration of oxygen.In addition,the oxygen vacancy will produce a deep donor defect level in the band,but it is difficult to improve the conductivity of the material.With the increase of oxygen vacancy concentration,the band gap width of defect structure will increase,and the distance between defect energy level and conduction band will also increase.Compared with the intrinsic?-Ga₂O₃structure,new peaks are introduced in the imaginary part of the dielectric function and the absorption spectrum of the oxygen vacancy defect structure,and the difference between the peaks coincides with the defect level in the band structure.In addition,the virtual part of dielectric function and the peak value of absorption coefficient will increase with the increase of oxygen vacancy concentration.?2?The crystal structures,electronic structures and optical properties of Ti-doped?-Ga₂O₃ with intrinsic defects are investigated by first-principle calculations based on density functional theory,and the compensation effect between Tidopant and intrinsic defects is discussed.Four defective structures of Ti-doped?-Ga₂O₃ include Ti_Ga2O3O_i?O interstitial?,Ti_Ga2O3Ga_i?Ga interstitial?,Ti_Ga2O3V_O?O vacancy?and Ti_Ga2O3V_Ga?Ga vacancy?.The calculation results show that Tidopant acts as an effective n-type dopant and makes the material more conductive.Besides,the defect formation energies of interstitial O and interstitial Ga are low under specific conditions,indicating that Ti_Ga2O3O_iand Ti_Ga2O3Ga_i are relatively stable.Interstitial O atom would compensate with Tidopant and reduce the n-type conductivity of material,while interstitial Ga can enhance the n-type conduction of Ti-doped?-Ga₂O₃.After Ti-doping,the intrinsic absorption edge shows a slight red-shift compared with intrinsic?-Ga₂O₃.In addition,the optical absorption edge of defective structures(except Ti_Ga2O3Ga_i)are red-shifted relative to Ti-doped?-Ga₂O₃.?3?Based on the density functional theory,the first principle calculations of the crystal structure,electronic structure and optical properties of?-Ga₂O₃ with different Al doping concentrations?1.25 at%,1.67 at%and 2.50 at%?were carried out.The newly formed Al-O bond of Al-doped?-Ga₂O₃ will be shorter than Ga-O of the corresponding position of?-Ga₂O₃,and the volume of the doped structure will also be reduced.In addition,the formation energy of Al doping in the Ga2 position of?-Ga₂O₃is smaller.When the Al atom is doped in the?-Ga₂O₃ structure,the top position of the valence band of the doping structure will shift to the m point.Strictly speaking,the material will change to the indirect band gap material.However,the Al-doped?-Ga₂O₃structure still shows the nature of direct band gap structure.The direct and indirect band gaps of Al-doped?-Ga₂O₃ structure increase with the increase of Al doping concentration,and the gap between the direct and indirect band gaps is also increasing.In addition,the band gap of Al-doped structure is mainly determined by the O-2p state of valence band and the Ga-4s state of conduction band,which is consistent with?-Ga₂O₃.The position of absorption edge of doped structure is determined by the band gap.With the increase of Al doping concentration,the virtual part of dielectric function and absorption coefficient of doped structure will shift blue.