Freestanding CVD boron doped diamond single crystals: A substrate for vertical power electronic devices?

The development of all-diamond devices for power electronics is attracting more and more interest as judged by the recent increase in the number of publications on the subject. Nevertheless most devices reported in the literature used coplanar or pseudo-vertical geometries which, although promising in term of breakdown voltage, have still a relatively high on-state resistance. This could be related to current crowding due the low cross-section p+ layer. Vertical configuration, which requires thick heavily doped substrates, is a possible alternative usually used in conventional semiconductors. In this study, chemical vapour deposition (CVD) diamond growth conditions allowing heavy boron doping over an important thickness are discussed. It was found that there is an optimal range of microwave power density (MWPD) for which reasonable doping efficiencies and growth rates can be obtained leading to hundreds of micrometers thick crystals with a doping level higher than 1020?cm-3. The crystal morphology was predicted thanks to a 3D geometrical model and a small addition of oxygen to the gas phase was efficient to avoid the appearance of undesirable crystals faces and keep the crystal integrity. Freestanding boron-doped diamond single crystals were eventually grown and characterized by secondary ion mass spectrometry (SIMS), Fourier transformed InfraRed (FTIR) spectroscopy, Raman spectroscopy, high resolution X-ray diffraction (HRXRD) and four-point probe measurements. The high quality of the synthetic crystals was confirmed exhibiting electrical resistivities as low as 0.26?O?cm illustrating that this material is suitable for the development of vertical power electronic devices.