Shoichi Uchiyama

GaN-based photocathodes with extremely high quantum efficiency

We have fabricated phototubes with photocathodes consisting of the Mg-doped GaN films. The spectral shapes of the response and the quantum efficiency (QE) strongly depend on the Mg-doping concentration. The calibrated QE of the photocathode is maximized to be 71.9% at a photon energy of 5.4 eV by a Mg-doping concentration of 3.0×1019cm−3. Consequently, a phototube with the GaN-based photocathode is realized to demonstrate a very high QE, more than 50% and sharp cutoff characteristic over three orders of magnitude.

Electron diffusion length and escape probabilities for cesiated and hydrogenated polycrystalline diamond photocathodes

Electron diffusion lengths and escape probabilities from cesiated and hydrogenated polycrystalline diamond photocathodes were estimated by comparing the photoemission spectral response characteristics between the experimental and calculated data. As a result, the diffusion length for the polycrystalline diamond film used in this study was estimated to be as long as approximately 50 nm. Estimated escape probabilities of 0.8 and 0.2 were also obtained for cesiated and hydrogenated surfaces, respectively. The results suggest that the cesiated surface has a true negative electron affinity while the hydrogenated surface has an effective negative electron affinity.