| In recent years,?-Ga2O3 have been vigorously developed in the field of photoelectric devices and power devices due to it's large band gap,high breakdown electric field strength and high electron saturation speed.Although great breakthroughs have been made in experiments,?-Ga2O3 has been restricted in device applications due to its low thermal conductivity and mobility.Pressure regulation and interface engineering has been regarded as two effective ways to tune the properties of materials.In particular,the?-Ga2O3/GaN heterojunction is widely used in related experiments,but the influence of this interface on the performance of ?-Ga2O3 has not been systematically studied.In this thesis,the first-principles calculation method was used to research the regulation of hydrostatic pressure on the thermodynamic and photoelectric properties of ?-Ga2O3,as well as the electrical,optical and charge transport properties of ?-Ga2O3/GaN interface,and explore the influence of this interface formed with GaN on the performance of ?-Ga2O3 devices.1.First,the basic properties of intrinsic?-Ga2O3 are studied.It is found that there are six Ga-O bonds with different bond strengths in three crystal orientations.the Ga1-O1 bond among a axis is the longest and the bond strength is the lowest.The elastic constants of ?-Ga2O3 satisfies the mechanical stability criteria.The main diagonal elements C11 and C44 of the elastic matrix are the minimum elastic constants that characterize the resistance to compression and shear,respectively,indicating that the chemical bond strength on the(100)plane is the lowest.?-Ga2O3 is a direct band gap semiconductor,the electron effective mass is about 0.234m0?0.258m0.2.Secondly,the thermodynamic and photoelectric properties of ?-Ga2O3 under pressure were studied.In the pressure range of 10?15 GPa,mutations are observed in the lattice constant,bond length and bond angle.In the range of 15?20 GPa,the elastic constant C66 of ?-Ga2O3 becomes negative,which does not satisfy the mechanical stability conditions.And there is a mutation in the pressure range of 10?15 GPa and 25?35 GPa on elastic constants.It was believed that?-Ga2O3 began to undergo a phase transition in the pressure range of10?15 GPa and extend to 35 GPa,indicating that?-Ga2O3 phase transition was induced under pressure.Under the hydrostatic pressure of 0?10 GPa,it is found that pressure can enhance the strength of chemical bonds,effectively increase the ductility of ?-Ga2O3,and improve its anisotropy.Research on the minimum thermal conductivity and Debye temperature found that pressure of 0?5 GPa can improve the thermal conductivity of ?-Ga2O3and increase its stiffness.The heat capacity and the coefficient of thermal expansion both increase exponentially with temperature and then reach saturation values.Under pressure,the saturation value of the heat capacity are same(3n R=124.7 J·mol-1·K-1),while the coefficients of thermal expansion continued to decrease,being 7.28×10-6,6.93×10-6 and6.8×10-6 K-1 at 0,5,and 10 GPa,respectively.Under hydrostatic pressure,the band gap of ?-Ga2O3 changes from direct to indirect.Both the band gap and the electron effective mass increase as pressure increases.For comparative research,the thermodynamic properties of GaN under pressure were studied at the same time.it was found that the elastic constants satisfies the mechanical stability conditions,and the thermodynamic parameters change smoothly as pressure changes.the coefficient of thermal expansion is lower than?-Ga2O3and the ductility is worse than?-Ga2O3.3.Finally,the photoelectric properties of the?-Ga2O3/GaN interface are studied.The 12kinds of interfaces have obvious interface states and interface polarization.The 6 kinds of N-terminated surface formed heterojunctions show TYPE?band structure,and electrons are accumulated on the GaN side,and the C1-N interface has the largest charge transport and less charge recombination,which is beneficial to improve the optical performance of ?-Ga2O3 devices.The band structures of another 6 kinds of Ga-terminated surface formed heterojunctions show downward bending,indicating that there is charge accumulation at the interface,and the differential charge densities shows that the charge accumulation is concentrated at the center of the interface,close to the?-Ga2O3 surface,The B2-Ga interface has the largest charge accumulation.The formation of a laterally transported charge accumulation layer on the?-Ga2O3 surface is expected to produce?-Ga2O3-based high-speed electronic devices.All interfaces significantly enhance the absorption of ?-Ga2O3 in the infrared and visible regions. |
PDF Full Text Request