Diffusion of Impurities Under Bias in CVD Diamond Films

The diffusion of oxygen, lithium, chlorine, and fluorine in CVD diamond films was performed under bias at 700 and 1000 °C. SIMS and Auger analyses were used to determine the impurity concentration. After diffusion, the concentrations of Li and O in the diamond films were found to be of the order of (3–4)×1019 cm-3. The fluorine concentration was of order of (l-2)×1017 cm-3. The conductivity was p-type. The change in the resistivity due to diffusion was nearly nine orders of magnitude for the sample diffused under electric field, and six orders of magnitude for the samples diffused without field. No dependence of the impurity concentration on the applied bias was observed except for fluorine. The fluorine concentration dependence on the electric field indicates that fluorine may have formed a shallow level in the diamond band gap. The fact that large concentrations of impurities can be diffused into diamond films at relatively low temperatures indicates the presence in the films of many lattice defects (including grain boundaries).