Extreme mechanical hardness, broad optical transparency and high electrical resistivity are the most known characteristics of diamond. As silicon, diamond is also a semiconductor usable for the fabrication of electronic devices. Compared to silicon, diamond has a higher electrical breakdown field, higher thermal conductivity and carrier mobility allowing the fabrication of compact devices operating at higher temperature, however the control of its electrical properties and its micro-processing is more complex than for silicon. Electrical properties of diamond can be tuned by the minute addition of boron or phosphorus atoms. The electrical conductivity of boron-doped diamond varies from very resistive to very conductive over 12 decades. Depending on its atomic boron concentration, doped diamond is used in the fabrication in electronic devices, e.g. high voltage Schottky devices, transparent conductive electrodes or electrochemical electrodes. Properties of fabricated diamond layers are determined using standard and advanced in-house characterization methods or within national and international collaborations include: scanning electron microscopy, atomic force microscopy, Raman spectroscopy, photoluminescence spectroscopy, Hall effect, transmission electron microscopy, nano-indentation, secondary ions mass spectroscopy, etc. In particular, due to its high potential application in electrochemistry and microelectronics researchers in the MNB group are investigating, in detail, electrical properties of boron-doped doped diamond. By a careful control of the deposition conditions, they are able to produce electrochemical electrodes with a wide potential window, low capacitance and good electron transfer kinetics. Using electrostatic discharge characterization techniques, i.e. transmission line pulse current-voltage measurement, they study the so far unexplored impurity impact ionization effect, and more general electrical properties of doped diamond at high electric field [MNB06]. Raman spectroscopy characterization method, which unambiguously allows the identification of diamond from non-diamond carbon. Researchers in the MNB group have demonstrated, by a careful analysis of characteristic Raman of boron doped diamond, determination of boron concentration in diamond using this simple, rapid and non-destructive method [MNB07].
(upper left): Comparison of silicon carbide and diamond growth rates vs process gas composition in Microwave Plasma Enhanced Chemical Vapour Deposition with linear antennas; (upper centre) Comparison of mechanical properties of silicon carbide (SiC), nanocrystalline (NCD),and boron-doped nanocrystalline diamond (NCD-B) layers vs silicon; (upper right) Bright field transmission electron microscopy image of a silicon carbide and diamond composite layer; (lower left) Electrical breakdown voltage in boron-doped diamond for different acceptor concentrations; (lower centre) Effect of crystal orientation on the Raman spectrum of heavily boron-doped epitaxial layers; (lower right) Electrical conductivity map of a 6-inch quartz wafer coated with boron-doped diamond.
[MNB06] V. Mortet et al., Conductivity of boron-doped diamond at high electrical field, Diam. Relat. Mater. 98 (2019) 107476 - DOI: 10.1016/j.diamond.2019.107476
[MNB07] V. Mortet et al., Determination of atomic boron concentration in heavily boron-doped diamond by Raman spectroscopy, Diam. Relat. Mater.93 (2019) 54 - DOI: 10.1016/j.diamond.2019.01.028
