Direct deposition of GaN-based photocathodes on microchannel plates

摘要

Epitaxial growth of p-type GaN-based UV photocathode by RF plasma assisted molecular beam epitaxy (MBE) onsapphire, fused silica, and alumina substrates was investigated. The electrical measurements indicted the growth ofhighly p-type GaN films as thin as 0.1 u.m on c-plane sapphire with a thin A1N nucleation layer. Polycrystalline p-typeGaN was obtained for growth on fused silica and alumina. Negative electron affinity (NEA) photocathodes werefabricated by cesium activation of the p-type GaN films in vacuum. Quantum efficiency for UV detection on differentsubstrates was then characterized. To study the integration of UV photocathodes with MCPs, direct deposition of p-typeGaN films on glass MCPs were done at low growth temperatures by MBE. The detection efficiency of polycrystalline p-GaN photocathodes in reflection mode was much less than the high quality p-type GaN films on sapphire, however, itwas comparable to the detection efficiency of the latter measured in the semitransparent mode. This indicates thepotential for fabrication of improved photocathodes with higher gain and better spatial and temporal resolutions.