The lattice diffusion coefficient of B in monocrystals was investigated at temperatures of between 450 and 1000C (table 9). The diffusivity (and solubility) was found to be considerably higher than the corresponding values for Si. It was proposed that the experimental data showed that the B-doped material could be described as a regular solution, in the dilute limit, with an enthalpy of solution of about -0.4eV. The experimental data, and theoretical estimates of the excess enthalpy of solution, indicated a weak interaction of B with the Si and Co atoms. It was suggested that the B atoms occupied sites in the lattice which made a small contribution to the Gibbs energy of the solution phase. The diffusion data revealed a high mobility of the B atoms; with an activation energy of about 2.0eV for lattice diffusion. This value was about 1.0eV lower than that reported for the self-diffusion of Si, Ge or Co in the present material. It was recalled that B was a small atom which could occupy interstitial sites in this relatively open structure, and it was suggested that the diffusion of B could occur via a mixed process in which interstitial and substitutional interchange occurred; including trapping and de-trapping of the B atoms.

C.Zaring, A.Pisch, J.Cardenas, P.Gas, B.G.Svensson: Journal of Applied Physics, 1996, 80[5], 2742-8

Table 9

Diffusivity of B in CoSi2