Photocathodes on Polycrystalline CsI/Na

Abstract

This chapter discusses photo cathodes on polycrystalline CsI/Na. It is difficult to make semitransparent photo cathodes on polycrystalline CsI/Na (hereafter denoted p-CsI/Na) having both high sensitivity and long life. When a photocathode is made on p-CsI/Na, the photocurrent, which is initially high, often decreases during operation. The two ways of producing the photocathode differ in the first process. The first step of one method is introduction of abundant alkali metal vapor to the p-CsI/Na. This process, called doping, is different from that used in forming conventional photo cathodes. To make K-Cs-Sb bi-alkali photo cathodes, potassium or other alkali metals are used for doping. The potassium is introduced in a heated dispenser at a constant substrate temperature and the system is evacuated. The composition of each oxide layer is variable according to which alkali metal is introduced and whether it is made of composite layers. It is then essential that, after deposition of alkali metal on the substrate is completed, oxygen can be introduced to oxidize the alkali metal.