First-principles Calculation And Solar Blind Photodetectors Research Of ?-Ga₂O₃

?-Ga₂O₃ has been reported second thermodynamically stable phase among the five polymorphs of gallium oxide,it has the advantages of large band gap,superior ferroelectric performance,and strong spontaneous polarization properties,which makes?-Ga₂O₃ in solar blind photodetectors and high-power electronic devices have broad prospects.First,this thesis analyzes the structure and electrical properties of?-Ga₂O₃ by first-principles calculations,then uses PLD technology to prepare?-Ga₂O₃ and?-Ga₂O₃thin films,compares and analyzes their material properties and optical characteristics,and finally studies the effect of annealing on the properties of?-Ga₂O₃ materials and solar blind photodetectors.First,we calculate the intrinsic?-Ga₂O₃ in the ideal case,and use the scissors operator method to modify the band structure to obtain the intrinsic?-Ga₂O₃ with a band gap width of 4.893 e V.The lattice constant after optimization calculation is basically consistent with the experimental value.The calculations for the possible Ga vacancies and O vacancies show that the presence of Ga vacancies will affect the size of the lattice constant,At the same time,the band gap width will be widened.The conduction band structure of the energy band structure is analyzed.It is found that number of energy levels of the conduction band of?-Ga₂O₃ in the presence of Ga vacancies is more than the intrinsic?-Ga₂O₃.Analysis of Sn-doped?-Ga₂O₃ shows that the replacement of Ga atoms and O atoms by Sn atoms will increase the lattice constant.This is because the atomic radius of Sn is larger than the atomic radius of Ga and O,resulting in lattice expansion and lattice constant increases.The substitution of Sn for Ga atoms will narrow the band gap of the material,but it is still a direct band gap semiconductor,while the replacement of O atoms not only narrows the band gap,but also indirect band gaps appear.By comparing the density of states,the total density of states after replacing Ga atoms and O atoms by Sn doping is lower than that of intrinsic DOS,indicating that the electron energy of the valence band is reduced after doping.Compared with the formation energy,it can be found that the formation energy of Sn instead of Ga atoms is much lower than that of O atoms,so after Sn enters?-Ga₂O₃,it will take the lead in replacing Ga as an impurity to form an n-type semiconductor.Secondly,the?-Ga₂O₃ and?-Ga₂O₃ films were grown on the sapphire substrate.XRD test results show that the grown films correspond to the diffraction peaks(201),(402)and(603)of the?-Ga₂O₃ and the diffraction peaks of the(0002),(0004),and(0006)of?-Ga₂O₃.By calculating the lattice coefficient,it is found that the addition of Sn element causes the tensile stress in the existence plane of?-Ga₂O₃,the diffraction peaks are slightly shifted to a large angle direction,and the full width at half maximum is reduced,indicating that the grain size is more larger,higher crystallinity.AFM test results show that?-Ga₂O₃exhibits columnar growth,and the surface roughness is greater than that of?-Ga₂O₃.The transmission spectrum test results show that both transmittances are above 70%,and the calculated optical band gaps of?-Ga₂O₃ and?-Ga₂O₃ are 4.92 e V and 4.81 e V,respectively.The test results of solar blind photodetectors show that the?-Ga₂O₃ detector has larger photocurrent and dark current than the?-Ga₂O₃ detector,and has a higher photo-dark current ratio(PDCR)and responsivity.This is because the Sn element exists in the form of ionic Sn⁴⁺and Sn²⁺in?-Ga₂O₃,one way of Sn⁴⁺is to replace the position of Ga³⁺,and the other is to enter the lattice with interstitial atoms,which both cause lattice distortion and ionize.The electrons make the conductivity of?-Ga₂O₃ stronger,and the dark current increases.Spectral response test results show that the band gap widths of?-Ga₂O₃ and?-Ga₂O₃ are 4.90 e V and 4.76 e V.This is because the doping of Sn element causes a large stress in the film,which reduces the band gap width.It can be concluded from the transient response results that the Sn element introduces more deep-level defects,which affect the generation and recombination of photo-generated carriers,reducing the response speed of the detector.The?-Ga₂O₃ film was thermally annealed respectively at 500°C,600°C,and700°C.The XRD test results show that annealing causes more residual stress to be released inside the lattice,causing the lattice to deform and anisotropic shrinkage of the lattice,so,it lead to the diffraction peaks to shift to large angles.The photodetectors test results show that annealing can make the dark current smaller and the photocurrent larger.This may be because high temperature annealing is more favorable for the recrystallization of the gallium oxide epitaxial layer,which leads to a reduction in oxygen vacancies and a better optical gain.The transient response results show that the annealing greatly increases the slow response time of the photodetector,further indicating that annealing causes more Sn elements to enter?-Ga₂O₃ to form deep-level defects.