New mechanism of impurity conduction in lightly doped crystalline noncompensated silicon

It is found that the plastic deformation of lightly doped crystalline silicon samples ($N<6\times10^{16}$ cm$^{-3}$) with a low compensation ($K\sim3\times10^{-2}$) gives rise to nonohmic conduction $\sigma_M$ in electric fields that differs radically from conventional hopping conduction via the ground states of impurities ($\sigma^3$). The values of $\sigma_M$ can exceed values of $\sigma^3$ by a factor of $10^3-10^5$. The value of $\sigma_M$ and its dependence on the electric ($E$) and magnetic ($H$) fields can be controlled by varying the density of dislocations and the mode of thermal sample treatment. A strong anisotropy of $\sigma_M$ is observed in samples with oriented dislocations: the conductivities along and across dislocations can differ by a factor of $10^4$. The results are explained by the occurrence of conduction via the $H^-$-like states of impurities concentrated in the vicinity of dislocations. The levels of these states lie between the upper and the lower impurity Hubbard bands.