Studies of a conductivity mechanism of β-rhombohedral boron in a strong electric field

The dependence of electroconductivity of pure β-rhombohedral boron on the temperature and the intensity of an electric field is presented. The results are discussed using three models: (I) the Poole-Frenkel model for an isolated trapping centre and for a screened Coulomb centre, (II) the hopping models of Mott and Shklovskii, and (III) the small polaron model. The results of the electric field measurements may be satisfactorily interpreted in both the screened Poole-Frenkel and the hopping model giving for the dependence of the conductivity σ on the electric field intensity E the relations (σ/σ0)1/2 In (σ/σ0) E and In (σ/σ0) E−1/4, respectively (σ0 is the conductivity in zero field). The model III alone gives an unreasonable result for the hopping length but nevertheless the essentiality of polaronic effect for β-boron seems sufficient from both the experimental and the theoretical point of view. It is supposed that the very complex crystal lattice of β-rhombohedral boron has a mixed conductivity of a polaron–Mott type. The magnetoconductivity of boron in the hopping region is also discussed.