High-Conductivity N-Type Diamond Demonstrated

Researchers at Centre National de la Recherche Scientifique's facilities in Meudon and Grenoble, France, Technion in Haifa, Israel, and the Naval Research Laboratory in Washington report in the July issue of Nature Materials that deuterating boron-doped diamond converts the material from P-type to N-type with conductivities as high as 2 S/cm at room temperature. The work potentially enables the construction of classical PN-junction devices, such as LEDs, in diamond.

The optical, chemical and thermal characteristics of diamond make it a desirable material for use in various electronic and optoelectronic devices. Although it had been known that the addition of boron makes it a P-type semiconductor, an N-type dopant that yielded diamond with useful electrical conductivities had remained elusive.

To produce the material, the researchers grew 500-nm-thick homo-epitaxial layers of boron-doped diamond on synthetic diamond substrates in a microwave plasma chemical vapor deposition system and exposed the samples to a microwave deuterium plasma at 550 °C for eight hours. Subsequent annealing under a vacuum at temperatures of 520, 600 and 650 °C for various durations led to changes in the electrical properties of the samples, including a return to P-type conductivity.