Fabrication of group III-nitride photocathode having Cs activation layer
View Patent ↗Improved photocathodes are provided by a fabrication method including steps of wet chemically cleaning the photocathode emission surface (to reduce the level of cleaning-induced surface damage), two stage heat treatment (to complete the cleaning without desorbing nitrogen from the emission surface), followed by activation with Cs only, as opposed to Cs—O. The resulting photocathodes have improved performance (lifetime, brightness, efficiency) compared to conventional photocathodes, and are thus attractive candidates for demanding photocathode applications.
1. A method for fabricating a photocathode, the method comprising:
providing a substrate including a light-absorbing region including a material having a composition AN, wherein A is a group III element or a mixture or alloy of group III elements, and wherein N is Nitrogen, and wherein a surface of the light-absorbing region is also an emission surface of the substrate;
chemically cleaning the emission surface with a wet chemical process;
heat treating the substrate after the cleaning, wherein the heat treatment includes a first phase preceding a second phase, wherein the second phase is at a higher temperature than the first phase, and wherein the temperature during the first phase is at least 300C;
activating the emission surface after said heat treating by providing Cesium (Cs) to the emission surface and by not providing Oxygen to the emission surface, whereby Cs-only activation is obtained.
2. The method of claim 1 , wherein said emission surface is exposed to a vacuum during said first phase.
3. The method of claim 2 , wherein said vacuum has a pressure of less than 5×10 −9 Torr.
4. The method of claim 1 , wherein said emission surface is exposed to an ammonia atmosphere during said second phase.
5. The method of claim 4 , wherein said ammonia atmosphere comprises 10-100 Langmuirs of ammonia having a purity of 99.9999% or greater.
6. The method of claim 1 , wherein said heat treatment includes a temperature ramp from 400 C to 700 C over a time span of an hour.
7. The method of claim 6 , wherein said emission surface is exposed to an ammonia atmosphere during said second phase, and wherein said second phase is the last ten minutes of said time span.