Forced diffusion of impurities in natural diamond and polycrystalline diamond films

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Abstract
A method is proposed for the determination of the state of an impurity (donor, acceptor, or deep level) in semiconductor lattice. To demonstrate the method boron was diffused into type Ia natural diamond under a dc electric field. The concentration and diffusion profiles of boron were affected by the applied field. Boron diffuses as a negative ion since it is an acceptor shallow enough to be partially ionized at the temperature of diffusion. The drift velocity of boron ions at the temperature of diffusion was also estimated. The diffusion of lithium and oxygen from a Li2CO3 source in chemical vapor deposited diamondfilms was performed under bias at 1000 °C in an argon atmosphere. After diffusion, the concentrations of Li, O, and H in the diamondfilms were found to be around (3–4)×1019 cm−3. No dependence of these concentrations on the applied bias was observed. It was found that the diffusion of Li goes primarily through grain boundaries, which may explain why it does not depend on the applied voltage. Fluorine was present as an impurity in the dopant source. Its concentration in the films was around (1–2)×1017 cm−3 and did depend on the applied bias, indicating that fluorine may have formed a shallow level in the diamond band gap.

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