Energy Bandgap Engineering of Transmission-Mode AlGaAs/GaAs Photocathode

Aiming to enhance the photoemission capability in the waveband region of interest, a graded bandgap structure was applied to the conventional transmission-mode AlGaAs/GaAs photocathodes based on energy bandgap engineering, wherein the composition in AlxGa1−xAs window layer and the doping concentration in GaAs active layer were gradual. According to Spicer’s three-step model, a photoemission theoretical model applicable to the novel transmission-mode AlxGa1−xAs/GaAs photocathodes was deduced so as to guide the cathode structural design. Then the cathode material was grown by the metalorganic chemical vapor deposition technique, and the epitaxial cathode material quality was evaluated by the means of scanning electron microscope, electrochemical capacitance-voltage, X-ray diffraction and spectrophotometry. Through a series of specific processes, the cathode material was made into the multilayered module, possessing a glass/Si3N4/AlxGa1−xAs/GaAs structure. After the surface treatment including heat cleaning and Cs▬O activation for the cathode module, the image intensifier tube comprising the activated cathode module, microchannel plate, and phosphor screen was fabricated by indium sealing. The spectral response test results confirm the validity of the novel structure for the enhancement of blue-green photoresponse

Exploring metal-supported few-layer graphene for photocathode application through Cs/O activation process

Exploring a photocathode with features of visible-light response, high quantum efficiency, long life-span, easy availability and low cost is the desire of electron source applications. Here, we report the photoemission behavior of nickel-supported few-layer graphene through Cs/O activation process. We observe that this Cs/O-activated graphene-based photocathode can possess a cut-off response wavelength of 750 nm, a quantum efficiency over 0.1% at 350 nm, and a 1/e operating lifetime of over 50 h under continuous mW-level laser irradiation at a pressure of 10-7 Pa. Importantly, the photoemission capability after degradation can be completely restored again to its original maximum through the additional Cs deposition process. Moreover, the changes in surface composition and work function characterized by in-situ photoelectron spectroscopy demonstrate the low work function and excellent stability. This metal-supported graphene material with low-work-function surface provides a route to obtain robust photocathode working from ultraviolet to visible waveband

Supplementary document for Enhanced blue-green response of nanoarray AlGaAs photocathodes for underwater low-light detection - 6515455.pdf

Table of underwater windows for various ocean water