Superconductivity in boron-doped homoepitaxial (001)-oriented diamond layers

The crystallinity and built-in strain of diamond epilayers grown by MPCVD with boron contents n(B) Varying from 2 x 10(20) to 2 x 10(21) cm(-3) as evaluated by SIMS are assessed by HR-XR Diffraction. Both ac transport and ac susceptibility measurements show that the critical concentration for the onset of superconductivity in (001)-oriented single crystalline films is about 5 x 10(20) cm(-3). This is also the critical hole concentration for the metal-non metal transition in this system, as evaluated by two types of theoretical calculations and by low temperature resistivity experiments. We report also preliminary results of point contact spectroscopy on an epilayer with a critical transition temperature T-c = 2.1 K, which yield a superconducting gap around 0.3 meV compatible with a conventional BCS-type description of superconductivity in this system. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.