A hybrid photodetector (HPD) with a III-V photocathode

A hybrid photodetector (HPD) combined with a III-V photocathode is considered to be an ideal photodetector, because the quantum efficiency (QE) is high, the collection efficiency is 100%, and the excess noise factor is negligible. An HPD combined with a GaAs photocathode or a blue enhanced GaAs (BE-GaAs) photocathode has been developed. Presently, the QE is approximately 20% from 550 nm to 850 nm, which is much higher than that of a conventional multi-alkali (S-20) photocathode. The 100% collection efficiency calculated by the computer simulation is supported by the test result of the flat uniformity. Considering the application in high energy physics using a wavelength shifter, energy resolutions of both the BE-GaAs-HPD and the conventional S20-HPD were measured using a 650 nm LED light pulse. The BE-GaAs-HPD shows a resolution of 17%, as against 34% for the S20-HPD. The experimental results are consistent with the theoretical estimation. The QE of the HPD is especially important, because the electron multiplication process is noiseless.