Research on Optical Properties for the Exponential-Doped Ga1-xAlxAs/GaAs Photocathode

To research the influencing factors in the optical properties of Ga_1-xAl_xAs/GaAs photocathode, one uniform-doped sample was prepared with the GaAs thickness of 2.00 μm and the Be-doping concentration of 1×10¹⁹ cm^-3, and two more exponential-doped samples were 2.00 μm and 1.60 μm in the thickness whose Be-doping concentration quasi-exponentially distributed ranging from 1×10¹⁸ cm^-3 to 1×10¹⁹ cm^-3. The optical properties curves were separately measured by use of the spectrophotometer. Based on thin film optical principles, matrix model of the optical properties is built for the four-layer photocathode module with a structure of Glass/Si₃N₄/Ga_1-xAl_xAs/GaAs. The result shows that the photocathode with low average doping concentration and large thickness has high absorptivity within the response waveband. According to integral sensitivity equation, the optimized GaAs thickness of the exponential-doped Ga_1-xAl_xAs/GaAs photocathode is simulated to be 2.00 μm.