Study And Simulation Of Semiconductor Characteristics And Surface Sensitization Of The Near-infrared InGaAs Photocathodes

InxGa1-xAs is an important III-V semiconductor.The negative electron affinity(NEA)can be generated through proper surface sensitization.The NEA InxGa1-xAs photocathode has a good spectral response in the near-infrared region(1?3 ?m),making sense for the new-type low-light-level(LLL)night vision system and near-infrared LLL image intensifier with high performance.However,a further theoretical study of InxGa1-xAs aiming to perfect the material properties is needed.The bulk characteristics of the substrate and emission layers,and the surface properties of the emission layer 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 InGaAs photocathodes.The GaAlAs buffer layer cannot solve the lattice mismatch completely between GaAs substrate layer and InGaAs emission layer.The GaAs quality will affect the growth of InGaAs emission and the photoemission of the NEA photocathode.The doping and the point defects of the GaAs substrate layer are studied.The p-type GaAs substrate layer is formed by Zn doping.The energy gap is narrowed down and the ionicity around the doped Zn atom is enhanced after doping.Six kinds of point defects,VAs,VGa,AsGa,GaAs,Asin and Gain,in GaAs substrate are put forward.The optical properties and the formation energy are analyzed.Three kinds of point defects:VGa,AsGa,Asin are proved to be generated more easily.The point defects move the spectral response of the GaAs substrate to long wave region.The lattice constant,energy bands and the optical properties of the InGaAs emission layer are changed with the variation of the In component x.In0.53Ga0.47As with 0.53 as In component is chosen for emission layer through the study of the characteristics of InxGa1-xAs with different In component.Bulk characteristics of the emission layer are very important to the InGaAs photocathode.However,the influence of doping and vacancy defects is not clear yet.The bulk properties of intrinsic InGaAs are studied and Zn is chosen as the substitution atom for doping.It is indicated that material characteristics are almost same and the p-type In0.53Ga0.47As photocathodes are both formed whether Ga or In atom is displaced.At the same time,the photoemission characteristics are changed from the combined impact of vacancy defects and Zn doping.It is pointed that As vacancy defect is the positive electricity centers and the acceptor levels are generated,which is benefit for the photoelectrons transport.The Ga and In vacancy defects generate indirect band gaps and should be avoided.The surface sensitization is the key to generate NEA photocathode.The thesis emphasizes on the study of surface sensitization mechanism.The photoelectrons transported to the surface will escape to the vacuum efficiently through the sufficient surface sensitization.There are relaxation and reconstruction on the In0.53Ga0.47As surface and it is confirmed that the ?2(2×4)surface is benefit for the surface sensitization.Then the reconstruction surface is doped and the properties are analyzed.It is pointed that Zn4 is the best doping position.The In0.53Ga0.47As ?2(2×4)with Zn doped in Zn4 position is taken as the sensitization base.The phenomenon of Cs poisoning is studied.It is indicated that the critical value of the Cs coverage degree is 0.5ML.After that Cs and O atoms are adsorbed alternately on the surface.Then the double dipoles,InGaAs(Zn)-Cs and Cs-O,are generated on the surface and the work function is reduced.Surface sensitization is realized and the photoelectrons escape to the vacuum effectively.