Received: October 23, 2007

In Final Form: December 5, 2007

Abstract:

-Rhombohedral (-rh) boron is the most stable polymorph of elemental boron at low temperatures and exhibits p-type semiconductive properties. Although -rh boron has some voids of sufficient size in its structure, it does not accept alkali metals as donor dopants. An n-type or metallic -rh boronlike material so far has not been found. We considered substituting Li for either of P or As in the stable -rh boronlike compounds B₁₂P₂ and B₁₂As₂ and calculated the electronic structures from first principles to investigate the possibility that -rh boron becomes an n-type semiconductor or a metal. The idea is similar to the case of diamond, where the codoping of a donor and acceptor creates an n-type semiconductor. Our results showed that B₁₂PLi and B₁₂AsLi became intrinsic narrow-gap semiconductors with band gaps of 0.478 and 0.536 eV, respectively. In both materials, the curvature of the conduction band was higher than that of the valence band, suggesting that the electron mobility may be higher than the hole mobility.

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