Preparation of Semiconducting Diamonds

P-type semiconducting diamonds can be formed at high pressures and temperatures out of mixtures of graphite and catalyst metal (Ni, Fe, etc.) to which small amounts of B, Be, or Al have been added. The crystals may have resistivities of as low as 103 ohm-cm with activation energies for conduction ranging between 0.1 and 0.35 ev. Semiconducting crystals may also be prepared by allowing B or Be to diffuse into diamond crystals at high pressures and temperatures. The crystals prepared with high concentrations of boron are blue. No n-type crystals have been prepared so far.