In this decade, studies on semiconducting diamond for the power device application have intensively been conducted in several research groups. A use of diamond crystals with low defect density is crucial for obtaining high blocking voltage. High crystalline quality and high purity of diamond crystals are also requested in the field of research on quantum information using diamond. Although a lot of effort was devoted to improve the quality of diamond films, dislocations still remain in the crystals with the number density higher than 10⁴ cm^-2. In this study, we propose advanced diamond growth condition that removes crystalline defects effectively during the growth process of homoepitaxial diamond films.

Homoepitaxial diamond films were deposited on Ib(100) substrates using the homebuilt microwave plasma-assisted chemical-vapor-deposition (MPCVD) apparatus [1]. In this study, effect of oxygen addition during diamond growth was investigated [2]. Typical growth condition was as follows; total gas pressure, microwave power, methane concentration (flow ratio of CH₄ to the total gas flow), oxygen concentration (flow ratio of O₂ to the total gas flow), and substrate temperature were 120‒140 Torr, 1.2‒1.4 kW, 4‒10%, 0‒2%, and 950‒1050 °C, respectively. Microwave power density estimated from the injected microwave power divided by the plasma volume was 110‒180 W cm^-3.

By optimizing growth conditions with higher oxygen concentration of 2%, high-purity homoepitaxial (100) diamond layers, typical nitrogen concentration of which was less than 1 ppb, were successfully grown. Cathodoluminescence mapping and 3D Raman measurements indicated a number density of dislocations in the homoepitaxial layer is typically 10⁴-10⁵ cm^-2. Tungsten carbide Schottky electrodes fabricated on the non-doped diamond showed high blocking voltage of 2.2 kV. This diamond films growth technique is promising for designing high-performance quantum information devices.

The author would like to thank Dr. T. Yamamoto, Dr. S. Koizumi, Dr. K. Watanabe, Dr. H. Umezawa, Dr. S. Onoda, Dr. O. Milikofu, Prof. F. Jelezko, and Prof. J. Isoya for helpful discussion and supporting characterization.

[1] T. Teraji, T. Yamamoto, K. Watanabe, Y. Koide, J. Isoya, S. Onoda, T. Ohshima, L. J. Rogers, F. Jelezko, P. Neumann, J. Wrachtrup, and S. Koizumi, phys. stat. sol. (a) 212, 2365(2015).

[2] T. Teraji, J. Appl. Phys. 118, 115304(2015).