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

Abstract

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 Ω cm illustrating that this material is suitable for the development of vertical power electronic devices.

Diamond Schottky diodes operating at 473 K

“…Specifically for vertical sample, studies show vertical defects in diamond explaining the lowest percentage of functionality with 75 % which is encouraging [15,16]. The different parameters measured are honorable and reproducible,…”

Low resistivity p+ diamond (100) films fabricated by hot-filament chemical vapor deposition

“…The preparation of p + substrates via MWPCVD suffers from several technical shortcomings such as the soot formation [12,17] and limited growth area [18][19][20]. These problems are still open issues.…”

“…B-doping is a well adapted technique to produce p-type conduction in diamond, and heavily B-doped (p + ) substrates have been fabricated via both high-pressure high-temperature (HPHT) gradient method [9,10] and MWP CVD [11,12]. In most of these attempts, the B concentration and the resistivity of the p + layers are limited to be less thañ 10 20 cm −3 and larger than 10 mΩ·cm, respectively.…”

Defect and Threading Dislocations in Single Crystal Diamond: A Focus on Boron and Nitrogen Codoping

“…Such free‐standing films could be used as substrates to fabricate high power vertical devices. Vertical Schottky diodes are typically obtained by growing a thin low boron‐doped film on a heavily boron‐doped substrate . In this case, the low‐doped film behaves as the active layer.…”