Manipulation of diamond surfaces using a two-photon laser technique for electronic applications

Diamond is an exceptional material with stable colour centres, a wide band gap, high thermal conductivity, and a unique surface. Engineering the termination, orientation, and defects of the surface is important for quantum computing and sensing, and electronic applications. Techniques for manipulating the surface include processes based on plasma, chemical, electron and ion beams, and laser treatments. We report the sub-monolayer manipulation of diamond surfaces using deep-UV laser processing. Laser pulses at 266 nm of fluence below the ablation threshold were used to oxidize the surface and remove carbon, through 2-photon-induced photo-chemical ejection, and the effects on the electrical and chemical surface properties were measured. It is found that the resistance of a hydrogen surface increases with the UV dose from 2 to 3 kΩ up to the measurement limit of 100 GΩ for doses corresponding to 0.5 monolayers, behaviour which agrees well with geometric and tunneling percolation arguments for the surface conduction. We also show that dosing before hydrogenation produced up to five times reduction in surface resistance and an increase in carrier concentration, and that these effects enable enhancement of the current density of diamond surface field effect transistors. We use XPS measurements of the surface chemistry as a function of dose to help elucidate the UV-induced mechanism responsible for enhancement.