Comparison between gradient-doping GaAs photocathode and uniform-doping GaAs photocathode

We compared two reflection-mode negative electron affinity (NEA) GaAs photocathode samples that are grown by molecular beam epitaxy with p-type beryllium doping. One sample is uniform doping, and another is gradient doping. Experimental curves of spectral response sensitivity and quantum efficiency are obtained. The thicknesses of the two cathodes are both 2.6 mu m. The integrated sensitivity of the uniform doping one is 1966 mu A/lm, and that of the gradient-doping one is 2421 mu A/lm. The escape probability and diffusion length are fitted from the spectral response curves. For the uniform-doping sample, the escape probability is 0.45 and the diffusion length is 5 mu m. For the gradient-doping sample, the escape probability is 0.55 and the diffusion length is 5.5 mu m. (c) 2007 Optical Society of America.