Impurity Ionization in Germanium in Strong Magnetic Fields

Low-temperature electrical breakdown in $p$-type germanium has been investigated at magnetic-field strengths up to 52 kOe. The electric-field strength required for the onset of breakdown in gallium-doped germanium increased from 4.2 V/cm at zero magnetic field to 22 V/cm in a 50-kOe transverse magnetic field. For a longitudinal magnetic field of the same range, there is a smaller variation of breakdown electric field with a maximum of 7.2 V/cm at 50 kOe. The effect is independent of the polarity of electric field applied to the specimen in all cases. The increase in electric field required for breakdown appears to be in reasonable agreement with recent theories of impact-ionization phenomena, provided that the quantization and shift of energy levels in a strong magnetic field are considered together with the effect of transverse magnetic fields on the rate at which carriers gain energy from an electric field. Measurements of the changes of the far-infrared photoconductivity of the specimen in the magnetic field provide further evidence of the effect of the field on the ionization phenomena.