The impact of ozone on the surface conductivity of single crystal diamond

Abstract The electron affinity and thereby the ionisation energy of single crystal diamond (100) is changed between −1.3 and +1.7 eV and 4.2 and 7.2 eV, respectively, by stepwise oxidation of hydrogenated surfaces in ozone-rich atmospheres. Simultaneous measurements of the surface conductivity (SC) demonstrate that even for slight oxidation the SC disappears in air whereas SC is fully maintained in an ozone-rich atmosphere up to a partial oxygen coverage of ∼40%. These results constitute the first observation of electron transfer to the O 3 /O 2 +OH − redox couple that extends on account of its lower electrochemical potential (compared to the H 3 O + /H 2 couple active in normal air) the SC to samples with electron affinities higher than that of the hydrogenated surface. Thereby, the results confirm the basic tenet of the electrochemical transfer doping model in which the ionisation energy of diamond and the electrochemical potential of aqueous redox couples govern the charge exchange that leads to SC by a subcutaneous hole accumulation layer. In a second set of experiments, it is shown that for samples annealed in vacuum at temperatures between 250 and 700 °C SC is lost and does not recover upon air exposure despite an intact hydrogen coverage of the surface. However, after a brief exposure to ozone that does not result in any measurable oxidation, SC is recovered upon exposure to air. Explanations of this effect in terms of ozone-induced catalytic centers or passivation of donor-like surface defects are being offered. The relevance of these results for similar observations in connection with UV illumination is being alluded to.