GaN (Cs)

III-V nitride semiconductors are in high demand in many application fields and have garnered increasing interest, especially since the Nobel Prize was awarded for developing the gallium nitride (GaN) light-emitting diode (LED) in 2014. As a potential photocathode, p-type III-V semiconductors have the extraordinary ability to form a negative electron affinity (NEA) surface when they are activated with a thin layer of alkali metal, such as cesium.

Compared to the existing photocathodes, p-GaN:Cs photocathodes offer many advantages:

- high quantum efficiency (QE) in the UV range

- more robust against vacuum issues

- longer lifetime

- negative electron affinity (NEA) surface can be achieved only with cesium

-  re-activation by a simple thermal vacuum cleaning

Different commercially availablep-GaN grown on sapphire by metal-organic chemical vapor deposition was wet chemically cleaned and transferred into an ultra-high vacuum chamber, where it underwent a subsequent thermal cleaning. The cleaned p-GaN samples were activated with Cs to obtain p-GaN:Cs photocathodes and their performance was monitored with respect to their quality, especially concerning their quantum efficiency and storage lifetime.
Treatments at different temperatures resulted in various quantum efficiency values of 1–12% and maximum storage lifetimes of about 5000 h.

The surface topography and morphology were examined ex-situ by atomic force microscopy and scanning electron microscopy in combination with energy dispersive X-ray spectroscopy.

GaN:Cs photocathode ©Copyright: Jana Schaber

left: GaN photocurrent curves during activation process; middle: SEM Image of used GaN:Cs photocathode; right: QE decay curves for each activation cycle

Foto: Jana Schaber



1046111002 TP A Beschleuniger - VP_DALI - FWKE

BMBF-Verbundprojekt 05K2016: HOPE-II


Schaber, J.; Xiang, R. et al. Influence of Surface Cleaning on Quantum Efficiency, Lifetime and Surface Morphology of p-GaN:Cs Photocathodes. Micromachines 13, 849, 2022.

Schaber J, Xiang R, Arnold A, et al.Impact of various cleaning procedures on p-GaN surfaces.Surf Interface Anal. 2023;1‐8.