Photoemission performance of thin graded structure AlGaN photocathode

Abstract

In order to research a high-efficiency AlGaN photocathode, the AlGaN photocathodes with varied Al composition (0.68 and 0.4) and uniform Al composition (0.24) were grown. The photocathodes were activated by Cs adsorption and received their spectral response via multi-information system. Results show that the absorption rate of the AlGaN photocathode with varied Al composition is half of the AlGaN photocathode with uniform Al composition, but the quantum efficiency of the photocathode with varied Al composition is approximately 29% higher than that of the photocathode with uniform Al composition. The built-in field within the emission layer of the AlGaN photocathode with varied Al composition is much higher than that of the photocathode with uniform Al composition, which is the main factor that promotes the photoelectron movement toward the photocathode surface and improves photoemission performance of the AlGaN photocathode.

Perspectives on Designer Photocathodes for X-ray Free-Electron Lasers: Influencing Emission Properties with Heterostructures and Nanoengineered Electronic States

“…In some cases, QEs of well over 20% have been reported for NEA treated GaN-based photocathodes under UV illumination. Various reports suggest that certain properties of GaN-based semiconductors can be tailored to enhance photoemission including band gap engineering 122,123 , doping 124,125 , utilizing inherent polarization fields 124 , nanowire structures 126 , quantum well structures 122,123 , and heterojunction schemes 119,127 . Some of these reports show promising results for limited application areas, but systematic investigations are lacking and there is limited information regarding photocathode lifetimes and no information on emittance measurements.…”

Electronic properties of graded Ga 1‐x Al x N superlattice nanowires photocathode: First‐principles

“…5,6 At present, regarding the material composition, the internal field introduced by the variation of structure can change diffusion length of the electrons and improve the quantum efficiency. 7,8 In particular, when this method is applied to a NW arrays photocathode, the generated internal field could effectively reduce electrons' shielding and divergence caused by transverse electrons in the cathode vacuum chamber. 9 GaAs photocathode with a strained superlattice structure can provide 92% spin polarization.…”

“…Although the pure NW arrays photocathode improves the photoemission capability, due to the contradiction between spin polarization and quantum efficiency, the performance cannot achieve a stable and stable growth 5,6 . At present, regarding the material composition, the internal field introduced by the variation of structure can change diffusion length of the electrons and improve the quantum efficiency 7,8 . In particular, when this method is applied to a NW arrays photocathode, the generated internal field could effectively reduce electrons' shielding and divergence caused by transverse electrons in the cathode vacuum chamber 9 .…”

The effective light‐harvesting performance of graded compositional Al x Ga 1−x N nano‐cone arrays photocathode for ultraviolet detector—A numerical investigation and simulation

“…Initially, in order to solve the lattice mismatch problem between the AlGaN emission layer and the AlN buffer layer, which causes the photoelectrons to recombine and shortens the electron lifetime, a buffer layer structure with graded Al composition is proposed . Then, the graded compositional Al x Ga 1−x N structure classifies the bandgap of the photocathode and generates a built‐in electric field inside the material, which can reduce the surface recombination loss and promote the photoelectrons to the surface of the emissive layer for the enhancement of quantum efficiency …”

“…In addition, the powerful axial built‐in electric field induced by the gradient bandgap material can effectively reduce the lateral emission phenomenon caused by the electron emission from the side of the nanowire array structure, which prevents electron emission angle divergence and spatial resolution degradation . The gradient bandgap structure has been introduced into photon‐enhanced thermal electron emission devices and UV detector devices to enhance electron emission from the top surface of the photocathode . Currently, we have designed a feasible method to prepare graded composition Al x Ga 1−x N nano‐cone array.…”