Study On The Surface Adsorption Characteristics Of The Group Ⅲ Nitride Cathode Material

With the development of semiconductor theory and the continuous progress of material growth process,group III nitride semiconductor materials mainly based on GaN/GaAlN can be adjusted within a certain range due to low dark current,high quantum efficiency,stable physicochemical properties and response light wavelength.It has been widely used in the fields of ultraviolet light detection,environmental monitoring,missile warning and fire monitoring.GaN semiconductor materials have the characteristics of wide band gap,high thermal conductivity,and high breakdown voltage.They are known as the third-generation semiconductor materials and are the most widely used photocathode materials in Group III nitride materials.GaAlN photocathode can adjust the composition of Al element to achieve variable response wavelength,which has been widely used in the field of solar blind ultraviolet detection and single photon detection.At present,the domestic and foreign research hotspots on GaN/GaAlN and other group III nitride photocathodes are mainly focused on structural design,high concentration doping experiments,surface activation,etc.This article mainly uses first-principles calculation methods from From the perspective of simulation,GaN/GaAlN and other cathode materials are simulated,and physical quantities that cannot be directly measured in traditional laboratories are calculated and analyzed.The specific research content is as follows:The Cs-GaN thin film structure and the Cs-GaN nanowire structure were established using Materials Studio software,and the changes of adsorption energy,work function,dipole moment,and atomic structure of two different structure adsorption models were compared and studied.The best Cs adsorption sites on the surface and the change trend and principle of the work function of the two structures under different Cs coverage conditions have a positive impact on the development and improvement of traditional thin film structures and new nanowire structures.During the Cs/O activation experiment on the GaAlN photocathode,we found that the GaAlN photocurrent increase during the Cs/O alternate activation phase is not obvious,while the photocurrent of GaAs/GaAl As during the Cs/O alternate activation phase can even increase by 4-5 times.This is because the GaAs/GaAl As crystal material is a zinc blende structure,and there are more groove structures on the adsorption surface,which can provide more space for the attachment of Cs/O atoms,and GaN/GaAlN belongs to the zinc blende structure.O atoms do not have enough space to attach,and the Cs-O dipole moment is parallel to the surface,the work function does not decrease significantly,and the activation efficiency is not high.On this basis,we established a Cs-GaAlN surface defect adsorption model.Due to the presence of defect sites,some O atoms can directly attach to the defect sites,forming a Cs-O dipole moment perpendicular to the surface of the material,effectively reducing the material The size of the surface work function further improves the quantum efficiency of the photocathode.The activation efficiency of the negative electron affinity photocathode has a great relationship with its photoemission performance.At present,the negative electron affinity photocathode is mainly obtained by adsorbing Cs/O atoms on the surface of the GaN/GaAlN photocathode.Grade clean surface is the key to improve the efficiency of photocathode activation.We finally studied the GaN/GaAlN surface cleaning process.A control experiment group was set up to analyze the chemical cleaning methods of GaN and GaAlN photocathode,and it was found that the concentrated sulfuric acid mixed solution can effectively remove the C and O impurities on the cathode surface,and the KOH solution can remove the aluminum oxide impurities on the GaAlN photocathode surface.In addition,chemical cleaning can only initially remove surface impurities.To achieve atomic-level cleaning of the surface,high-temperature thermal cleaning is required.We have conducted a detailed study of the mechanism of photocathode thermal cleaning,and the analysis shows that high-temperature thermal cleaning has a major impact on the surface and interior of the material.Remove impurities.Finally,the best thermal cleaning temperature experiment of GaAlN photocathode was set,and the GaAlN photocathode with the lowest resistivity was obtained at about 850 ℃.