UV photoemission efficiency of polycrystalline CVD diamond films

Abstract

The absolute quantum efficiency of polycrystalline diamond films grown on silicon substrates by chemical vapor deposition (CVD) is reported in the range of 25–200 nm. The efficiency of boron-doped and hydrogen-activated by microwave plasma reflective photocathodes peaked at 37% at 40 nm with the sensitivity cutoff observed at ∼190 nm. We confirmed that hydrogen activation is relatively stable in air: the efficiency of the photocathode degraded by less than 15% after an 18-h air exposure. It was found that diamond photocathodes can be reactivated multiple times to the same high QE values even after extended ultrasonic cleaning in both water and alcohol. The sensitivity of a diamond photocathode coated with a high dipole moment 4-nm-thick CsI layer was found to be slightly better than that of hydrogenated films, especially at longer wavelengths, while the sensitivity cutoff shifted to ∼200 nm. The observed high efficiency of thin CVD diamond films and relatively high stability of surface activation makes them a very attractive alternative to many existing UV photocathodes, especially taking into account other useful features of diamond (mechanical and chemical stability and radiation hardness).