This thesis describes the development of a gallium arsenide (GaAs) photocathode preparation facility (PPF) with a load-lock interface as part of an upgrade to the ALICE photo-injector electron gun. The PPF has the capacity to prepare up to six negative electron affinity (NEA) GaAs photocathodes, and permits the rapid and reliable replacement of the degraded photocathode in the gun, while maintaining the integrity of the gun vacuum system. The photocathode preparation has been studied and developed using a custum-built surface characterisation system which permitsthe preparation of NEA GaAs photocathode in conjunction with the application ofseveral surface science characterisation techniques within the same vacuum system. With GaAs/AlGaAs hetero-structure photocathodes designed and developed in collaboration with the Institute of Semiconductor Physics (ISP/Novosibirsk), quantum efficiencies (QE) of 15 - 19% at 635 nm and long lifetimes of the order of 6,800 hours are achieved in a reproducible way. Using the PPF, I have investigated the degradation in the QE of NEA GaAs photocathodes under exposures to gases typically present in the gun vacuum, namely O2, CO2, CO, H2, CH4 and N2. The effects of these gases on the NEA GaAs photocathodes have been demonstrated for the firrst time in a vacuum set-up with a base pressure in 10E-11 mbar range. It was found that H2, CH4 and N2 have no effect on the photocathodes lifetime, whilst substantial reductions of the QE have been observed during the exposures to O2, CO2 and CO. It was also demonstrated for the first time that the NEA GaAs photocathode activated with Cs and NF3 is more stable during CO2 and CO exposures than the photocathode activated with Cs and O2.

Ce travail de thèse, effectué en collaboration avec la société PHOTONIS, un des leaders mondiaux dans la conception de tubes intensificateur de lumière, et l'Institut d'Électronique du Sud de l'Université de Montpellier, a pour but l'optimisation des photocathodes de 3e génération à base d'(In)GaAs pour lunettes de vision nocturne. Après avoir décrit le principe d'un tube intensificateur de lumière et présenté les performances atteintes par ces différentes générations de dispositifs, le cas plus spécifique de la photocathode est abordé. Par la simulation des performances, deux structures photocathodes sont proposées. L'une pour la détection des faibles niveaux de lumière résiduelle dans le visible, l'autre pour l'extension de la réponse spectrale vers le domaine du proche infrarouge (λ=1,06µm). Le processus technologique pour la fabrication de photocathodes de hautes performances est décrit étape par étape puis les caractérisations électro-optiques, associées aux composants réalisés, sont présentées. Les résultats obtenus montrent des performances en termes de réponse spectrale qui dépassent régulièrement les 1600µA/lm. / This thesis reports on the optimization of 3rd generation photocathode based on (In)GaAs materialfor night vision google. It is realized in collaboration between the PHOTONIS Company, one of the world leaders in conception of image intensifier and the Institut d'Électronique du Sud from Montpellier University. After a description of an image intensifier operation and a presentation of the state of the art of the image intensifier devices, the more specific case of the photocathode is described. Two photocathodes structures are deduced from simulation of performances, one for detection of low levels of visible residual light and the other for infrared extension of spectral response (λ=1.06µm). The different steps of the technological process for the manufacturing of high efficiencies photocathodes are described and the electro-optical characterizations made are presented. The results show performances as hight as 1600$µA/lm.