Microstructure,Electronic Band And Temperature-Variable Properties Of Si/Mg Doped β-Ga₂O₃ Single Crystals

β-Ga₂O₃ has important application prospects in high-power,high-voltage electronic devices,ultra-deep ultraviolet detection,and other fields due to its unique advantages such as ultra-wide band gap and high breakdown field strength.It is one of the research hotspots of ultra-wide band gap semiconductor materials in recent years.Doping is a key technology in the development of Gallium Oxide-based semiconductor devices.For Gallium Oxide single crystals,Si doping forms an effective n-type semiconductor,while Mg doping reduces its conductivity and forms a semi-insulating semiconductor.Doping will not only change the electrical properties such as carrier concentration ofβ-Ga₂O₃ crystal,but also have important influences on its microstructure and optical properties.At present,there are many studies on the electrical properties,but the effects of doping on the crystal microstructure,lattice vibration,optical properties and temperature change characteristics are lack of systematic research in doped gallium oxide single crystal.Therefore,a variety of spectroscopic characterization techniques are used in this paper to systematically analyze Si,Mg and unintentionally dopedβ-Ga₂O₃ single crystals.The main research results are as follows:（1）Si and Mg doping have important effects on the microstructural properties.Compared with unintentionally dopedβ-Ga₂O₃ single crystals,Si（Mg）doping causes the（400）,（600）and（800）interplanar spacings to decrease（increase）inβ-Ga₂O₃ single crystals.The Ga:O atomic ratio of Si/Mg doped Ga₂O₃ changes,and Si doping introduces more O vacancies.（2）The Raman scattering spectroscopy study found that compared with the unintentionally dopedβ-Ga₂O₃ single crystal,the Si dopedβ-Ga₂O₃ single crystal lattice is mainly subjected to compressive stress;while the Mg dopedβ-Ga₂O₃ lattice is mainly subjected to tensile stress.According to the analysis of Raman spatial correlation model,doping reduces the crystal perfection and short-range order of the crystal,among which the propagation length of the A_g^（10）phonon mode of the unintentionally dopedβ-Ga₂O₃ single crystal is the longest,while Mg doping is the shortest.In addition,each Raman phonon mode exhibits the characteristics of partial linear polarization,but the degree of polarization is obviously different.In the high wavenumber region,the Raman phonon modes with poor polarization of Si,Mg doped and unintentionally doped samples are A_g^（10）,A_g^（8）and A_g^（10）,respectively;in the middle wavenumber region,the polarization properties of the four phonon modes of the Si doped and unintentionally doped samples are all good,and only A_g^（6）has better polarization in Mg doped samples;and there are two dominant vibration directions for B_g^（2）of Si doped and unintentionally doped samples in the low wavenumber region.（3）In the temperature range of 80-800K,the Raman phonon modes of the three single crystals occur red-shift with the increase of temperature,and the Raman shifts and half-width broadenings of all phonon modes vary with temperature,which induces complex lattice expansion and nonlinear resonances.The correlation length of A_g^（10）phonon modes of the three single crystal samples decreased with the increase of temperature,and the correlation length of the unintentionally doped samples mostly changed,indicating that their internal microstructural properties were more sensitive to temperature changes.（4）Doping with Si and Mg brings about changes in defect energy levels and electron energy bands.The threeβ-Ga₂O₃ single crystals exhibited different defect luminescence properties,among which the Mg doped samples introduced more deep defect levels near the valence band and emitted stronger red light.The exciton activation energies of Si（Mg）dopedβ-Ga₂O₃ single crystals in the violet and red bands were obtained by analysis.At room temperature,the band gaps of Si,Mg and unintentionally dopedβ-Ga₂O₃ single crystals are 4.63 e V,4.78 e V,and 4.70 e V,respectively.Si doping reduces the band gap,while Mg doping increases the band gap.In 10K-300K variable temperature,the change of the band gap with temperature satisfies the Varshni formula,and the change of the band gap of Si doped single crystal is relatively small.The fermi levels of Si,Mg and unintentionally dopedβ-Ga₂O₃ single crystals are 0.32 e V,1.84e V and 0.67 e V from the conductive bottom,respectively.The fermi level of Si dopedβ-Ga₂O₃ single crystal is close to the bottom of the conduction band,showing n-type semiconductivity,while the Mg doped sample is close to the middle of the forbidden band,and its conductivity is semi-insulating.