The First Principle Study On Oxygen Adsorption Based On Gaas Alloy Materials

Al_0.5Ga_0.5As materials have been widely used in many fields owing to their excellent properties.However,a major drawback of Al_0.5Ga_0.5As materials is whose surface can be oxidized easily,and the surface states are produced,which seriously affects the photoelectric properties and stability of the devices.So far,many experimental reports have demonstrated the surface states of the Al_0.5Ga_0.5As surface,lacking the theoretical calculation,instead.In the view of this question,this dissertation studies the following contents through the method of the first principle calculation based on density functional theory?DFT?,with the quantum-mechanics program Vienna Ab Initio Simulation Package?VASP?.Firstly,the structures of Al_0.5Ga_0.5As and Al_0.5Ga_0.5As?001??2?2×4?are built.The electronic and optical properties of bulk Al_0.5Ga_0.5As and its?001?surface with?2?2×4?phase are calculated separately.Compared with the bulk material,the surface structure has a smaller band gap,both of the main absorption peak and absorption edge of the absorption spectrum are moving to the lower energy side,the peak value of absorption peak is decreased and the reflectivity is lower.The differences in the electrical and optical properties of the surface and bulk indicate,the importance of studying the surface properties of Al_0.5Ga_0.5As?001??2?2×4?.Then,12 kinds of the structure of the oxidized Al_0.5Ga_0.5As?001??2?2×4?surface are built.The electronic and optical properties of the oxidized Al_0.5Ga_0.5As?001??2?2×4?surface are calculated.The structure of adsorption of oxygen doesn't produce the band-gap states.However,the structure of substitution of oxygen has the band-gap states,due to the unsaturated As dangling bands.The gap state of the oxidized structure leads to the absorption peak appearing in the range of 0¹ eV,and the average reflectivity is greater than the clean surface,which will seriously hinder the generation of photoelectrons.The changes of the electrical and optical properties of the oxidized surface of Al_0.5Ga_0.5As?001??2?2×4?show that,the band-gap states affect the characteristics of the material surface seriously.Finally,the structures of the Al_0.5Ga_0.5As?001??2?2×4?surface with S and N passivated are built separately.The DOSs of the Al_0.5Ga_0.5As?001??2?2×4?surface structure with passivation are calculated.S passivation could partially eliminate the gap state,but its passivated structure is easy to be oxidized again.N passivation can vanish the Fermi level pinning,and weaken or eliminate the surface states completely.The changes of DOS in the passivated structures indicate that the passivation has the effect of eliminating the gap state of the oxidized surface.Through theoretical calculation,the origin of surface states produced by surface oxidation and the influence of passivation on the oxidized surface are shown,which provides the theoretical basis for eliminating surface state on the surface of the material,then improving the photoelectric properties and stability of the device.