Resolution characteristics of varying doping and varying composition Al_<i>x</i>Ga_1<i>–x</i>As/GaAs reflective photocathodes

Abstract

According to the established resolution model and modulation transfer function (MTF) of varying doping and varing composition reflection-mode (r-mode) Al_<i>x</i>Ga_1<i>–x</i>As/GaAs photocathode, the resolutions of four types of r-mode photocathodes, i.e. linearly varying doping and linearly varying Al composition, uniform doping and linearly varying Al composition, linearly varying doping and uniform Al composition, uniform doping and uniform Al composition structures, are simulated, and the effects of Al composition, the types of doping, Al_<i>x</i>Ga_1<i>–x</i>As layer thickness, GaAs layer thickness, and incident light wavelength on the resolution of cathodes are analyzed. The simulation results indicate that the varying doping and varying band-gap structures can also upgrade the resolution for r-mode Al_<i>x</i>Ga_1<i>–x</i>As/GaAs photocathodes, and the effect of linearly varying doping and linearly varying composition structure are more pronounced. The simulation results also show that the MTFs of the cathodes with the Al composition varying from 0.45 to 0 linearly declining are highest. The MTFs of the cathodes with the linearly varying doping from 10¹⁹−10¹⁸ cm^–3are higher than that with uniform 10¹⁹ cm^–3 doping. With the increase of Al_<i>x</i>Ga_1<i>–x</i>As thickness, GaAs thickness and incident light wavelength, the MTFs of four types photocathode have different regularities.