Photoemission characteristics of diamond ®lms

In this study, we investigate the photoelectric emission from CVD diamond ®lms. These diamond samples present NEA properties due to their as-grown surfaces terminated with hydrogen atoms. Photocathodes are characterised by UV pulsed laser-induced photoelectric measurements and photoelectric threshold measurements because the photoelectric emission is strongly dependant on the electron af®nity of the diamond surface. Photoelectric threshold measurements 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 ®lm. Moreover, the quantum ef®ciency of undoped diamond is measured at 213 nm as a function of the CH4 concentration. The highest quantum ef®ciency value is measured for the highest defect-density diamond ®lm. Surface bonds modi®cations occurring during a prolonged laser irradiation are responsible for the decrease in the photoemissive performances of diamond ®lms. # 2000 Elsevier Science B.V. All rights reserved.