AVS 53rd International Symposium
    Electronic Materials and Processing Thursday Sessions
       Session EM-ThP

Paper EM-ThP14
Decay Mechanism of Negative Electron Affinity (Cs/O Activated)InP(100) Photocathodes

Thursday, November 16, 2006, 5:30 pm, Room 3rd Floor Lobby

Session: Electronic Materials and Processing Poster Session
Presenter: D.-I. Lee, Stanford University
Authors: D.-I. Lee, Stanford University
Y. Sun, Stanford Synchrotron Radiation Laboratory
Z. Liu, Stanford Synchrotron Radiation Laboratory
S. Sun, Stanford University
P. Pianetta, Stanford Synchrotron Radiation Laboratory
Correspondent: Click to Email
Negative Electron Affinity (NEA) III-V photocathodes prepared by Cs and oxygen co-deposition have been widely used in technological applications of image intensifiers and e-beam sources due to its beam properties such as high quantum efficiency (Q.E), high spin-polarization, and low energy spread. One of the concerns raised in the usage of these photocathodes is the relatively short lifetime since industry desires that photocathodes last for a long period of time without losing its reliable performance. This lifetime issue is induced by the fact that very thin Cs oxide layer is extremely sensitive to contamination, which destroys the NEA properties of the surface and reduces its Q.E. The lack of understanding of the very thin Cs oxide activation layer, however, prevents researchers from providing a profound way to achieve long-lifetime stability especially when the photocathode is not in a sealed tube. In this study, we have investigated the decay mechanism of Cs/O activated InP(100) photocathode by Synchrotron Radiation Photoemission (SR-PES) and Energy Distribution Curve (EDC) measurements. We found that decay of Q.E. and the increase of electron affinity are due to the transformation of Cs peroxide into Cs superoxide and subsequent oxidation of InP substrate. These changes can be explained by thermodynamics. Furthermore, a simplified lateral distribution model of Cs oxide layer on the surface is proposed based on the angular dependence of O1s and valence band spectra. The redeposition of Cs was performed in order to simulate the sealed photocathode tube, and it is found that redeposited Cs recovers Q.E. by building up partial dipoles, and prevents Cs peroxide from transforming into Cs superoxide by acting as a protective layer.