Magnetic field effects on the nonohmic impurity conduction of uncompensated crystalline silicon

The impurity conduction of a series of crystalline silicon samples with the concentration of major impurity $N\approx3\times10^{16}$cm$^{-3}$ and with a varied, but very small, compensation K was measured as a function of the electric field $E$ in various magnetic fields $H-\sigma(H, E)$. It was found that, at $K<10^{-3}$ and in moderate $E$, where these samples are characterized by a negative nonohmicity ($d\sigma(0, E)/dE<0$), the ratio $\sigma(H, E)/\sigma(0, E)>1$ (negative magnetoresistance). With increasing $E$, these inequalities are simultaneously reversed (positive nonohmicity and positive magnetoresistance). It is suggested that both negative and positive nonohmicities are due to electron transitions in electric fields from impurity ground states to states in the Mott–Hubbard gap.