New pecularities of the conductivity and photoconductivity mechanisms in β-rhombohedral boron

The development of the steady-state dc conductivity of β-rhombohedral boron requires large temperature-dependent time constants (for example τ ∼ 5 h at 425 K) and exhibits stochastic precipitous jumps, whose height depends on temperature as well. At low temperatures, these jumps are attributed to trapping and releasing of electrons. At high temperatures, considering the unsteady changes of numerous physical properties between 500 and 600 K, the results are explained by the diffusion of interstitial B atoms causing statistical fluctuation of conductivity paths below the percolation threshold. The time-dependent photoconductivity measured between 88 and 576 K for times up to 45 h is strongly influenced by traps reducing the lifetime of the initially generated electrons considerably. This changes, when the trap occupation increases because of persisting optical excitation. Though under final stationary conditions the concentration of conducting electrons is independent of time, the conductivity persists to change; depending on temperature it increases or decreases. This is probably due to the diffusion of interstitial B atoms as well.