Photoemission characteristics of diamond films

In this study, we investigate the photoelectric emission from CVD diamond f ilms. These diamond samples present NEA properties due to their as-grown su rfaces terminated with hydrogen atoms. Photocathodes are characterised by U V pulsed laser-induced photoelectric measurements and photoelectric thresho ld measurements because the photoelectric emission is strongly dependant on the electron affinity of the diamond surface. Photoelectric threshold meas urements show the existence of a sub-bandgap signal associated to a defect- band level for both samples, with the lowest value obtained for the highest defect-density diamond film. Moreover, the quantum efficiency of undoped d iamond is measured at 213 nm as a function of the CH4 concentration. The hi ghest quantum efficiency value is measured for the highest defect-density d iamond film. Surface bonds modifications occurring during a prolonged laser irradiation are responsible for the decrease in the photoemissive performa nces of diamond films. (C) 2000 Elsevier Science B.V. All rights reserved.