Effects of graded band-gap structures on spectral response of AlGaAs/GaAs photocathodes.

The effects of AlGaAs/GaAs layer thickness and Al composition range on the spectral response and integral sensitivities of reflection-mode graded band-gap AlGaAs/GaAs photocathodes have been investigated and simulated. The experimental results demonstrate that the spectral response over the wavelength region of interest for graded band-gap photocathodes is greater than that for uniform band-gap cathodes, and the increase in long-wavelength response is more pronounced. These results can be attributed to the built-in electric field in the graded band-gap AlGaAs layer. We established a spectral response model of graded band-gap photocathodes based on the numerical solution of coupled Poisson and continuity equations. According to the model, we calculated the theoretical spectral response and sensitivities of graded band-gap cathodes, and found the optimum Al(x)Ga(1-x)As layer thicknesses are 6, 10, 16, and 22 μm for the reflection-mode cathodes with linearly graded Al composition x ranges of 0 to 0.1, 0.2, 0.3, and 0.4, respectively.