Field-assisted In_xGa_1-xAs Photocathode Body Material Properties Simulation Study

In Ga As is an important short-wave near-infrared photocathode material.In order to break the response wavelength threshold limit and improve the quantum efficiency near the long-wave threshold,a series of researches have been carried out on field-assisted In Ga As photocathode,which is of great significance for the preparation of photodetector devices with longer threshold wavelengths.In this paper,the bulk properties of the substrate and emission layer(photon absorption and photoelectron emission are implemented in the active layer),and the electronic structure and optical properties of the In_xGa_1-xAs active layer under the external electric field are studied using the first principles calculation method based on the density functional theory(DFT),which provides theoretical support and guidance for the development of In Ga As photocathodes.In this paper,the doping of In P substrate is calculated and analyzed.After Zn doping,the Fermi level enters the valence band,the energy gap is narrowed down and the ionicity of the material is enhanced,and In P becomes a p-type conductive material.The electronic structures and optical properties of the In_xGa_1-xAs active layers with different In composition were calculated.The results show that as the In composition increases,the average reflectance gradually decreases,and the absorption coefficient moves in the direction of the long wave.According to the strain and dislocation density caused by lattice mismatch,the critical thicknesses of In_xGa_1-xAs epitaxially grown on In P substrates with different In composition were calculated,the lattice matching relationship between In_xGa_1-xAs and In P substrates with different In compositions was obtained.Considering the lattice matching relationship between In_xGa_1-xAs and In P substrates and the effect of the selection of In composition on the band gap and optical properties of In_xGa_1-xAs,it is pointed out that when In composition is 0.53,In_0.53Ga_0.47As is suitable active layer material.The electronic structure and optical properties of the intrinsic In_0.53Ga_0.47As active layer are calculated.The results show that In_0.53Ga_0.47As is a direct bandgap semiconductor material.In_0.53Ga_0.47As can be doped with Be or Zn to obtain p-doped In_xGa_1-xAs materials.By comparing the formation of the Zn-doped model and the Be-doped model,it can be found that the structure of the Zn-doped model is more stable.The atomic and electronic structures of In_0.53Ga_0.47As materials were compared under two different doping methods:Zn replaced In and Zn replaced Ga.The results show that the effects of these two doping methods on the electronic structure of In_0.53Ga_0.47As materials are almost consistent,can form a suitable p-type conductive material,can be considered without distinction.The optical properties of Zn-doped In_0.53Ga_0.47As materials are calculated.The results show that Zn-doping can improves the absorption coefficient of In_0.53Ga_0.47As materials in the near-infrared band,which enhances the material's ability to absorb photons.Apply electric field to the In_0.53Ga_0.47As active layer,and the changes of the electronic structure and optical properties of the In_0.53Ga_0.47As active layer with the electric field were analyzed.Firstly,the influences of electric field directions such as(100),(010),(001),and(011)on the total energy and stability of the In_0.53Ga_0.47As active layer system were calculated.The results show that the system under the(100)direction electric field has the lowest total energy and the most stable structure.Apply electric fields of different strengths along the(100)direction,by comparing the band structure of the In_0.53Ga_0.47As active layer under different electric fields,it is found that as the external electric field increases,the bottom of the conduction band and the top of the valence band move to the low-energy side at the same time,but the amount of movement at the bottom of the conduction band is greater than the top of the valence band,so the band gap gradually narrows.The absorption coefficient of the In_0.53Ga_0.47As active layer in the near-infrared band increases with the increase of the external electric field,and its threshold wavelength extends to the long wave direction;The average reflectance decreases with the increase of the electric field intensity,which is beneficial for photons to pass through the surface to excite photoelectrons.