| Popis: |
A field‐assisted photocathode has been made which has a reflection yield quantum efficiency of ∠1% out to a wavelength of 1.6 μ. The cathode is a heterojuncation InP/InGaAs/InP structure fabricated by a hybrid VPE/LPE process. Photoelectrons generated for wavelengths ?1 μm must cross a p‐InP/p‐InGaAs heterojunction, under bias. To achieve high transfer across the p–p heterojunction, the heterojunction must be carefully lattice matched, the InP emitter must be ?1 μm thick and have p‐type doping in the low 1015 cm−3 range, the InGaAs layer must have doping in the low 1016 cm−3 range, and the heterojunction composition grading distance must be ?1000 A. These criteria are all met by the VPE/LPE grown heterojunction. Heterojunction transfer efficiencies approaching 100% for bias voltages 3–5 V have been measured. |
