No abstract

The fundamental Raman mode of diamond has been measured as a function of P and T up to 15 GPa and 400 °C. The calculated values of pressure coefficient (2.64 cm−1/GPa) and temperature coefficient (0.9×10−2 °C/GPa) of diamond show that this material can be used as a pressure sensor in a diamond anvil cell at high temperature. The Grüneisen coefficient (γ) is calculated and found to be equal to 0.9. From this value of γ, the atomic volume of diamond is obtained in the whole range of pressure and temperature.

The fabrication of diamond-based vertical power devices which are the most suited for high current applications requires the use of thick heavily boron-doped (B-doped) diamond single crystals. Although the growth of thin B-doped diamond films is well controlled over a large concentration range, little is known about the growth conditions leading to heavily doped thick single crystals. In this paper, it was found that the microwave power densities (MWPD) coupled to the plasma used to synthesize B-doped diamond by chemical vapor deposition is one of the key parameters allowing tuning doping efficiencies over two orders of magnitude. At high MWPD (above 100 W cm−3) the boron doping efficiency (DE) is extremely low while further increasing the boron concentration in the gas phase is no use as this leads to plasma instability. On the other hand, when low MWPD are used (<50 W cm−3), DE can be strongly increased but twinning and defects formation hampers the surface morphology. The use of intermediate MWPD densities has been demonstrated as the key in obtaining thick heavily B-doped diamond crystals (>1020 cm−3) with good morphologies.