Research on AlGaAs Photocathode with Enhanced Response at 532 nm

The AlGaAs photocathode can be used in the field of underwater optical communication because of its characteristics of fast response speed and adjustable spectral response range. In order to solve the problem that the low light absorption of the AlGaAs emission layer limits the improvement of its quantum efficiency, the distributed Bragg reflector (DBR) structure was used to reflect the light at a specific wavelength back to the emission layer to further increase the absorption rate, thus improving the response capability of the photocathode at 532 nm. The spectral response model of the AlGaAs photocathode with DBR structure was obtained by solving the one-dimensional continuity equation. The optical model of the AlGaAs photocathode with enhanced response at 532 nm was established by the finite-difference time-domain method. The effects of the sublayer periodic pairs, the sublayer material and the thickness of emission layer and buffer layer on the absorption rate of emission layer were analyzed. The light absorption distribution of AlGaAs photocathode with or without DBR structure was compared, and the influence mechanism of DBR structure on the blue-green light absorption capacity of AlGaAs photocathode emission layer was clarified, which could provide a theoretical basis for the design of its structural parameters. The results show that the DBR structure with the periodic pair of 20 and Al_0.7Ga_0.3As/AlAs has the best reflection effect on 532 nm light. Based on the DBR structure, when the thickness of the emission layer and buffer layer is 495 nm and 50 nm, respectively, the emission layer has the best absorption rate of 532 nm light. Furthermore, two kinds of AlGaAs photocathodes with or without DBR structure were grown by the metal-organic chemical vapor deposition technology, and the reflectivity and profile structure of the grown samples were characterized. Then the Cs/O activation experiments were performed to compare the spectral response curves. It is found that the spectral response of the AlGaAs photocathode sample with DBR structure at 532 nm wavelength is about twice that of the sample without DBR structure.