The paper describes a process of p-type to n-type conversion of diamond by deuterium diffusion. The results open an interesting research area in experimental and theoretical physics as well (detailed origin of the conductivity, atomic description of the deuterium-related donors, electronic transitions associated with these donors etc). In addition, the fabrication of highly conductive n-type diamond is a key technology for applications in the field of electrochemistry, field emission and high frequency electronics.

Pure diamond is strongly insulating. However, diamond containing suitable impurities (named donor dopants or acceptor dopants) is a highly promising semiconductor for high-temperature, high-power, and high-frequency electronics, because of its exceptional combination of electronic properties. A role of these dopants is to provide the free charge carriers (electrons for n-type materials and holes for p-type materials) necessary to ensure the flow of the electrical current in diamond. Up to now, the best donor dopants giving rise to electron related electrical conductivity were phosphorus atoms, but the amount of free electrons provided by these atoms was extremely small at room temperature. Consequently, the electrical conductivity of these phosphorus-doped diamonds was very weak and these diamonds are useless for electronic applications at 20°C. We have shown that, by diffusing deuterium in p-type boron-doped diamond, we are able to form new donor dopants at very high concentrations with new electronic properties. Consequently, the amount of free electrons provided by these donor dopants can be very high. The electrical conductivity of this deuterated boron-doped diamond is now well above that of phosphorus-doped diamond and should make it suitable for electronic applications.

I started working on the physics of hydrogen in crystalline semiconductors in 1984 when I was spending a sabbatical year with ATT Bell Laboratories at Murray Hill. In 1997, I moved to the problem of hydrogen in diamond showing the diffusion of hydrogen and the passivation effect of acceptors working in close collaboration with Alain Deneuville at LEPES CNRS, Grenoble, and Rafi Kalish and Cécile Saguy at Technion, Haifa, Israel, who already had strong experience on the growth of diamond and the physics of its defects. Then, we benefitted from the high-quality boron-doped diamond from Jim Butler of the Naval Research Laboratory in Washington, D.C., to succeed in getting the p-type to n-type diamond conversion. My Ph.D. student, Zéphirin Teukam, discovered this conversion effect at CNRS, Meudon and a patent was applied for in December, 2002.