GaAs negative electron affinity photocathode preparation by atomic hydrogen

Abstract

Summary form only given, as follows. Negative electron affinity (NEA) GaAs photocathodes are widely used in imaging tubes such as image intensifiers, streak cameras and photomultipliers, and recently proposed for applications in electron beam lithography and NEA-based microelectronics. GaAs activation to NEA requires an atomically clean crystal surface which is obtained by a chemical process followed by heating in ultrahigh vacuum. In this work, we prepare GaAs(100) NEA photocathodes by atomic hydrogen bombardment. Atomic hydrogen is known to cause a homogeneous desorption of carbon and oxide contaminants from GaAs surfaces, which can replace the chemical cleaning process and reduce the GaAs cleaning temperature. The preparation of the photocathodes by atomic hydrogen is performed at 450/spl deg/C while the conventional heat cleaning is performed at 600-700/spl deg/C. The high temperature cleaning causes preferential desorption of As and can destroy the photocathode. The samples are then activated to NEA by alternately depositing cesium and oxygen to maximize the photoemission. Cesium and oxygen are known to reduce the vacuum level below the bulk conduction band minimum producing a NEA surface with high quantum efficiency (QE) defined as the number of emitted electrons per incident photon. When we exposed the photocathodes to atomic hydrogen before activation, a QE of /spl sim/8.3% and /spl sim/5.3 % was produced when excited with 632.8 nm and 780 nm lasers, respectively. For a current of 1 /spl mu/A, the QE is reduced by /spl sim/25% after continuous operation for 13 hours.