Study And Similation On Characteristic Of Alkali-antimonide Photocathode

Alkali-antimonide photocathode has a simple way of preparation technology, lowcost, and short response time. It has relatively high sensitivity in the range of visibleand infrared (multialkali photocathode during300nm to850nm, while bialkaliphotocathode300nm to650nm). It is widely used in photoelectric device such asMCP(microchannel plate), streak camera and PMT(photomultiplier tube), has anirreplaceable role in the field of high-speed photography, single photon detection.This paper first carried on the theoretical modeling and simulation for multialkaliphotocathode. The stucture of photocathode was employed with layered model:Na2KSb+K2CsSb+Sb·Cs dipole layer. Effect of the thickness and doping concentrationof each layer to the energy band, build-in electric field and spectral response characterhave been discussed. The result shows that the doping concentration will influence thescope and intensity of the built-in electric field directly. Due to the build-in electric field,the excitation photoelectron will take diffusion and drift motion simultaneously, whichexpand its motion distance. It makes electron have higher probability reach the surfaceof photocathode. The highest sensitivity is got when doping concentration is about1016cm-3. Surface layer could lower electron affinity, the heavier of the dopingconcentration the better. While during the preparation, thinner film of surface layer isneeded. The thickness of photocathode could balance the absorption and diffusionprocess, and affect sensitivity and peak wavelength, for a certain wavelength incidentlight, there exist the optimum thickness.According to the photoelectron emission process, discussed the measurements toincrease quantum efficiency. Then calculated the optical properties of bialkaliphotocathode, designed anti-reflective layer to enhance incident light utilization. Effectof the anti-reflective thickness and refractive index was analysed, while cathodethickness is25nm, the optimum layer was obtained when its refractive is2.5, thicknessis30nm, interface reflectivity reduced from22%to4%, absorption enhanced from58%to73%，and discussed how to select the material. In the case of incident light incidentangle is less than50°, the reflectivity with the increase of the incidence angle can be ignored.To make full use of incident light, transmission plus reflection photocathodedesign was adopt in large area photomultipliers, in this case is analyzed and discussed.