Doping of diamond by in-diffusion of lithium in natural type Ia and IIa single crystal diamond plates was investigated. The lithium incorporation was realized by direct in-diffusion from a Li2O source at temperatures between 400 and 650C. Using secondary ion mass spectroscopy depth profiling, high concentrations of lithium, up to a level of 8.0 x 1021/cm3 and gradually decreasing to 1.0 x 1019/cm3 at a depth of 0.5μm below the surface, were measured. From these profiles the diffusion constant of lithium in diamond was found to be described by:

D (cm2/s) = 2 x 10-10exp[-0.9(eV)/KT]

The activation energy for diffusion of 0.9eV was in agreement with the theoretical literature value of 0.85eV. Cathodoluminescence spectroscopy showed that the blue band-A luminescence, which was characteristic for natural type IIa diamond, was largely quenched by the presence of lithium. A shift of the maximum luminescence intensity towards higher energy values was found. From photothermal deflection spectroscopy and optical transmission measurements no new optically active defect was observed after lithium in-diffusion. However, these measurements indicated the occurrence of a large concentration of light scattering centres, the size of which was 10nm or less. This suggested that lithium was clustered in the crystal volume just below the specimen surface and therefore was not electrically active.

Incorporation of Lithium in Single Crystal Diamond: Diffusion Profiles and Optical and Electrical Properties. Te Nijenhuis, J., Cao, G.Z., Smits, P.C.H.J., Van Enckevort, W.J.P., Giling, L.J., Alkemade, P.F.A., Nesládek, M., Remeš, Z.: Diamond and Related Materials, 1997, 6[11], 1726-32