Surface quality and composition dependence of absolute quantum photoyield of CVD diamond films

The absolute quantum photoyield (QPY) of polycrystalline diamond films in t he range of 140-210 nm is reported, for undoped and B-doped films, as a fun ction of deposition conditions and postgrowth surface treatment. B-doping, as well as geometrical structure, crystalline size and quality of the depos ited films did not affect the photoemission properties, whereas exposure to microwave (MW) hydrogen plasma significantly improved the QPY to more than 12% at 140 nm, compared to 4-6% measured for untreated films deposited by hot filament chemical vapor deposition (HFCVD) at temperatures of greater t han or equal to 900 degrees C, Undoped diamond films deposited by the MW pl asma chemical vapor deposition (MWCVD) at the same temperature showed a QPY of similar to 12% at 140 nm without additional hydrogen plasma treatment. A reduction in deposition temperature in the HF reactor resulted in an incr ease of QPY up to 11%. We have observed a decrease of the QPY in time, down to QPY values of 5-6%, for samples exposed to ambient air. The decrease oc curred on time scales of hours to weeks, for non-hydrogenated and postgrowt h hydrogenated films. The high QPY values were regenerated by repeating the hydrogenation process. The degradation of hydrogen-terminated films was fo und to be related to the adsorption of small amounts of oxygen, as detected by Auger electron spectroscopy. The observed oxygen adsorption at room tem perature is in contrast to that in previous studies, claiming the stability of hydrogen-terminated diamond surfaces. (C) 1999 Elsevier Science S.A. Al l rights reserved.