Electronic Structure And Physical Properties Of Doped Ga₂O₃

Wide band gap semiconductors have many advantages,such as high efficiency photoelectric conversion,excellent high frequency power characteristics,stable high temperature performance and low energy loss.They have become the key materials to support the development of information,energy,transportation,manufacturing and national defense.Ga2O3 is a promising wide band gap semiconductor.Its excellent material properties include extremely wide band gap(Eg?4.9 eV)and high breakdown electric field(8 MV/cm),making it especially suitable for solar blind photodetector(SBPD)and high power field effect transistor(FET).This thesis relies on the National Natural Science Foundation of China(approval number:11547039,61675032),the main research contents of this thesis include:1)Research on the basic physical properties of two-dimensional?-Ga2O3.Based on GW+RPA and GW+BSE method,the geometrical structure,electronic structure,optical properties and exciton properties of two-dimensional ?-Ga2O3 were studied.The results of geometric optimization show that the crystal structure of two-dimensional ?-Ga2O3 is distorted,the symmetry of the crystal decreases,and the electronic structure of the two-dimensional ?-Ga2O3 is affected.The exciton effect of two-dimensional ?-Ga2O3 is very obvious,which dominates their optical properties.We analyse that the decrease of Coulomb shielding of two-dimensional materials leads to the enhancement of exciton effect.2)Study on the basic physical properties of H-?-Ga2O3.Based on GW+RPA and GW+BSE methods,the regulation effect of H passivation on two-dimensional ?-Ga2O3 was studied.The exciton binding energy,maximum absorption coefficient and corresponding energy values were obtained accurately.H passivation will affect the geometry and electronic structure of two-dimensional ?-Ga2O3,and change with the number of layers.After passivation,the material tends to be more insulating.From the absorption coefficients calculated based on GW+BSE,the absorption coefficients of 1L,2L and 3L in the three polarization directions are all 105 cm-1 order of magnitude.In the three polarization directions of xx,yy and zz,the absorption peaks of GW+BSE are obviously red-shifted relative to the absorption peaks calculated by GW+RPA,and there are absorption peaks in the energy range below the band gap of the basic electron band,which indicates that H-?-Ga2O3 has strong exciton effect.3)Basic physical properties of bulk ?-Ga2O3 and Si doped ?-Ga2O3 were studied.The first Brillouin region,the high symmetry point and the high symmetry point path of the Brillouin region of the bulk ?-Ga2O3 are accurately obtained.The band gap(4.67 eV)and the density of states are modified by GW0 method.The effective mass of electrons in the energy band at point_is calculated.They are almost isotropic and their values are between 0.27 me and 0.28 me.The results show that the exciton effect in bulk ?-Ga2O3 material is very obvious and dominates its optical properties.We also calculated the exciton binding energy and the position and intensity of the maximum absorption peak.When Si is heavily doped,?-Ga2O3 becomes an indirect bandgap material.The absorption band edges ascended more slowly for Si-doped ?-Ga2O3 than undoped one.The main innovations of the thesis include:(1)The bulk and two-dimensional ?-Ga2O3 are studied by multi-body perturbation theory based on GW approximation.The energy band structure of bulk ?-Ga2O3,two-dimensional nanostructure ?-Ga2O3 and hydrogenation passivated two-dimensional ?-Ga2O3 is calculated by GW0.We also obtain their accurate band structure,band gap,density of states and electrons and hole effective mass,etc.(2)On the basis of accurately predicting the electronic structure,the bulk phase and two-dimensional ?-Ga2O3 expansion studies are calculated based on the GW+BSE method.The optical properties and exciton effects of bulk ?-Ga2O3,two-dimensional nanostructure ?-Ga2O3 and hydrogenation passivation of two-dimensional ?-Ga2O3 provide good theoretical support for the fabrication of optoelectronic devices based on?-Ga2O3.