The degradation of quantum efficiency in negative electron affinity GaAs photocathodes under gas exposure

Kinetics of alkali-based photocathode degradation

“…7,10,12 Many authors quote 1/e lifetimes without determining whether the degradation curve is exponential. 8,11,12,15 Some attempts have been made to introduce a more practical and universal metric for the lifetime by integrating pressure over time to obtain exposure expressed in Langmuir units. 6,10,11 Only one study conducted for (NEA) GaAs photocathodes provides reliable data that correlates QE with the time and the pressure of individual gases.…”

“…8,11,12,15 Some attempts have been made to introduce a more practical and universal metric for the lifetime by integrating pressure over time to obtain exposure expressed in Langmuir units. 6,10,11 Only one study conducted for (NEA) GaAs photocathodes provides reliable data that correlates QE with the time and the pressure of individual gases. 11 These materials owe their high QE under visible illumination to a monolayer of Cs-based dipoles produced during the surface activation process.…”

“…6,10,11 Only one study conducted for (NEA) GaAs photocathodes provides reliable data that correlates QE with the time and the pressure of individual gases. 11 These materials owe their high QE under visible illumination to a monolayer of Cs-based dipoles produced during the surface activation process. 13 Besides investigating this previous report, in this Letter we present QE degradation data on a representative sample of another class of photocathodes, the alkali antimonides that we fabricated and measured.…”

Photocathodes for near infrared range devices based on InP/InGaAs heterostructures

“…After heating in a vacuum chamber at a temperature of about 573 K, the net emitter atomic surface was received, that is ready for the activation with Cs and O 2 , which allows to form effective state of NEA on photocathode surface. The method of the activation structure called «yo-yo» [12], based on a continuous simultaneous supply of cesium and oxygen was used. The process for obtaining the maximum photoemission current was about 90 minutes.…”

Differences in stability and repeatability between GaAs and GaAlAs photocathodes

“…Currently, an important practical limitation of NEA photocathodes of concern is the limited lifetime of the NEA surface which requires that the NEA preparation is repeated [9][10][11]. Despite some similarities in the activation process of GaAs and GaAlAs photocathodes [12,13], there are few reports on comparison of the difference in photoemission degradation between them under the same preparation conditions.…”