Phase diagram of boron-doped diamond revisited by thickness-dependent transport studies

International audienceWe report on a detailed study of the electronic properties of a series of boron-doped diamond epilayers with dopant concentrations ranging from 1.10^ 20 to 3.10^21 cm −3 and thicknesses (d ⊥) ranging from 2 µm to 8 nm. By using well-defined mesa patterns that minimize the parasitic currents induced by doping inhomogeneities, we have been able to unveil a new phase diagram differing from all previous reports. We show that the onset of superconductivity does actually not coincide with the metal-insulator transition in this system. Moreover a dimensional crossover from 3D to 2D transport properties could be induced by reducing d ⊥ in both the metallic non-superconducting and superconducting epilayers, without any reduction of Tc with d ⊥ in the latter