A large number of sharp peaks are observed in the derivative magnetoresistance of high-purity n-GaAs and InP at 4 K with electric field biases slightly less than those required to produce impact ionisation of the shallow donors. The peaks are caused by inelastic scattering of the few electrons in the conduction band by the neutral donors. A series of peaks are observed with compensated samples whose peaks move rapidly to higher magnetic field with increasing bias voltage. These peaks are believed to arise from an impact excitation process whereby the impurity is left in an excited state after a collision and subsequently ionises by the absorption of a phonon. The second set of peaks observed is due to the magneto-impurity effect. A wide range of excited states are involved in high-purity materials, and in the case of InP, nearly one hundred peaks can be detected. Fine structure is found on the fundamental (highest field) peak of the strongest series and is correlated with the centraltell structure observed on the far-infrared magneto-optical transitions between the shallow donor states in the same material.
Hall voltage of n-InSb biased close to impact ionisationGlasgow G4 ONG, UK.
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