Study Of Preparation And Performance For Near-infrared InGaAs Photocathode

One of the important topics in the front field of photocathode in vacuum-type photodetector is to extend their response spectrum into long wavelength(near infrared).To achieve this purpose,we presented two kinds of InGaAs photocathodes with GaAs and InP substrates respectively,which are used to cover the common laser wavelengths 1.06 ?m,1.54?m and 1.57 ?m.The researches on surface model,photoemission process,quantum efficiency theory,structural design,preparation technology and performance evaluation of InGaAs photocathode were carried out in this thesis,which would promote the development of near infrared detection technology for our country.Based on the first principle of pseudopotential method,the optical properties on state density,dielectric function and complex refractive index of Zn-doped InGaAs photocathode were obtained.The calculations of light absorption,reflection and transmission were established by the theory of optical thin film.The Cs-O adsorption model was built according to the photoemission mechanism of NEA photocathode.Surrounded the Spicer's "Three-step Model",the energy distributions of electrons transporting in the body,reaching the surface and emitting into vacuum were calculated.By solving one-dimensional minority carrier continuous equation,the quantum efficiency formula of the reflection-mode InGaAs photocathode with thin emission layer was deduced.By fitting the experimental curves,the quantum efficiency factors were obtained,which include the surface escape probability,electron diffusion length,back interface recombination velocity and the thickness of emission layer.According to the strain and dislocation density caused by lattice mismatch,the critical thickness of InGaAs epitaxial layer with GaAs and InP substrates were calculated.Considering the epitaxial layer thickness,doping behavior,doping concentration,In mole fraction of InGaAs photocathode,the structure of InGaAs photocathode was designed with varied component and doping in order to reduce the lattice mismatch and improve photoemission performance as well.After that,the photocathodes were epitaxial growth by MOCVD.The system of photocathode preparation and evaluation were upgraded which expend the test range of light.The 1.06 ?m monochromatic light and X-ray electron spectrometer,were added to realize the real-time acquisitions of photocurrent,vacuum degree and Cs-O flux.By combining the results of XPS and Ar+ sputtering,the growth quality of InGaAs photocathode was identified.Then,the cleaning effects of different chemical methods and thermal purification temperatures were analyzed by XPS.According to the variations of the vacuum degree curves,the atoms desorptions and the thermal purification were researched.The performances of InGaAs photocathodes prepared by different preparation techniques were evaluated,the results showed that the InGaAs photocathode fisrt cleaned by a mix solution of carbonic acid and water for 2 min,and then "flash evaporation" at 625 ? could could achieve a good photoemission performance.In order to reseach the effects of Cs adsorption on the height of surface barrier,the changing of the response cutoff wavelength for Cs only exposure.Besides,the stabilities of reflection-mode InGaAs photocathode illuminated by different intensity light and multi-recaesiated after decay in the ultra-high vacuum activation system were evaluated.Finally,the performance of our reflection-mode InGaAs photocathodes was better than that of Hamamatsu company with 8.5 mA/W at 1.0 ?m and 0.51 mA/W at 1.06 ?m.