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

Abstract

The absolute quantum photoyield (QPY) of polycrystalline diamond films in the range of 140–210 nm is reported, for undoped and B-doped films, as a function of deposition conditions and postgrowth surface treatment. B-doping, as well as geometrical structure, crystalline size and quality of the deposited 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 ≥900 °C. Undoped diamond films deposited by the MW plasma chemical vapor deposition (MWCVD) at the same temperature showed a QPY of ∼12% at 140 nm without additional hydrogen plasma treatment. A reduction in deposition temperature in the HF reactor resulted in an increase 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 occurred on time scales of hours to weeks, for non-hydrogenated and postgrowth hydrogenated films. The high QPY values were regenerated by repeating the hydrogenation process. The degradation of hydrogen-terminated films was found to be related to the adsorption of small amounts of oxygen, as detected by Auger electron spectroscopy. The observed oxygen adsorption at room temperature is in contrast to that in previous studies, claiming the stability of hydrogen-terminated diamond surfaces.