Study On Electronic Structure And Optical Properties Of β-Ga₂O₃ Doped With ⅣA Elements

As a new type of oxide wide bandgap semiconductor with a theoretical band gap of 4.9 eV,β-Ga₂O₃ is widely used in power devices,optoelectronic devices,and gas-sensitive sensors because of its high critical breakdown field strength and high UV and visible light transmission.In this paper,in view of the lack of comparative studies on the electronic structure and optical properties ofβ-Ga₂O₃ doped with group IVA elements in experimental and theoretical calculations,and the difficulty of poor comparability of the final results due to the influence of various factors such as defects and background impurities when studying the problem experimentally,so we theoretically study the effect of group IVA elements on the electronic structure and optical properties ofβ-Ga₂O₃ by using the hybrid density function theory calculation method,in order to reduce the background impurity concentration inβ-Ga₂O₃ more effectively and regulate the carrier concentration ofβ-Ga₂O₃more precisely.The research contents,results,and main conclusions of this paper are as follows.（1）Using the Hybrid functional HSE06,the problem that the conventional GGA-PBE would underestimate the semiconductor band gap was corrected by adjusting the mixing parameters,and the intrinsicβ-Ga₂O₃ band structure with a direct band gap of 4.93 eV and an indirect band gap of 4.89 eV was obtained,the calculated effective mass of electrons at the Conduction Band Minimum was 0.27-0.28 m_e,while theValence Band Maximum was flatter than the conduction band minimum,This indicates that the hole effective mass of intrinsicβ-Ga₂O₃ is quite large.The density of states results show that the valence band of intrinsicβ-Ga₂O₃ consists of O-2p and Ga-3d,Ga-4s,and Ga-4p states,and the valence band has partial hybridization of Ga-4s and O-2p,the conduction band consists of Ga-4s and O-2p states.The optical property calculations show thatβ-Ga₂O₃ has optical anisotropy and high UV and visible transmittance,The optical bandgap size relationship between the three crystal direction of a[100],b[010]and c[001]is b>a>c.（2）The electronic structure and optical properties of group IVA elements C,Si,and Ge dopedβ-Ga₂O₃ were studied on the premise of theoretical intrinsicβ-Ga₂O₃ properties obtained from the calculations.The results show that C,Si,Ge all tend to replace the atoms in the C,Si,and Ge Ga（Ⅰ）positions when dopedβ-Ga₂O₃,and the bond lengths are all reduced compared to the intrinsic Ga-O bond lengths.The formation energy calculations show that the doping is easier under oxygen-rich atmosphere conditions,and the structural stability after doping is Si>Ge>C,both C and Si are shallow dopants,while Ge is a deep dopants.The Electron Localization Function shows thatβ-Ga₂O₃ is a semiconductor with ionic and covalent bonds coexisting,and the C-O is covalent,Si-O is ionic,the covalent bond strength of Ge-O is weaker than C-O and stronger than Ga-O bond.The electronic property calculation results show that the band gap of C,Si,Ge doped with different concentrations ofβ-Ga₂O₃’s bandgap at 3.125 at.%and 6.250 at.%will become smaller and the Fermi energy level will enter the conduction band,the larger the doping concentration,the narrower the bandgap and the deeper the Fermi energy level.In addition,as the radius of C,Si,and Ge atoms increases,the s-electron states contribute more to the conduction band below the Fermi level,which also leads to the decreasing effective mass of electrons at the Conduction Band Minimum.For the optical properties of C,Si,Ge dopedβ-Ga₂O₃ with 3.125 at.%concentration,Burstein-Moss and multibody bandgap renormalization effects lead to the increase of the optical bandgap,the optical bandgap value is Si>Ge>C,and the absorption coefficient of 253 nm UV light decreases after doping,the reflectivity also decreases,and the absorption edge shifts to the high-energy（short-wave）direction,making doping also enhancesβ-Ga₂O₃’s absorption in visible and infrared light,while the visible and infrared light absorption of Si-dopedβ-Ga₂O₃ is the strongest,indicating that the carrier concentration of Si onβ-Ga₂O₃ at the same doping concentration is more significant than that of C and Ge,and the relationship between the magnitude of conductivity is Si>Ge>C.