Low dimensionality of the surface conductivity of diamond

Walter Schottky Institute, Technische Universita¨t Mu¨nchen, Am Coulombwall 4, 85748 Garching, Germany(Dated: November 1, 2013)Undoped diamond, a remarkable bulk electrical insulator, exhibits a high surface conductivityin air when the surface is hydrogen-terminated. Although theoretical models have claimed thata two-dimensional hole gas is established as a result of surface energy band bending, no definitiveexperimental demonstration has been reported so far. Here, we prove the two-dimensional characterof the surface conductivityby low temperature characterization of diamond in-plane gated field-effecttransistors that enable the lateral confinement of the transistor’s drain-source channel to nanometerdimensions. In these devices, we observe Coulomb blockade effects of multiple quantum islandsvarying in size with the gate voltage. The charging energy and thus the size of these zero-dimensionalislands exhibits a gate voltage dependence which is the direct result of the two-dimensional characterof the conductive channel formed at hydrogen-terminated diamond surfaces.