High Field Magnetotransport: Lectures I and II: Analysis of Shubnikov de Haas Oscillations and Parallel Field Magnetotransport
The study of high field magnetotransport, and in particular the Shubnikov-de Haas effect, is one of the most useful and direct ways of characterising semiconductor heterostructures. At low temperatures a two dimensional gas of carriers bound in a heterostructure acts like a metal with a small Fermi energy, typically of order 10-100 meV. The magnetic field causes a quantisation of the free carrier states into a ladder of Landau levels. Changing the magnetic field sweeps the levels through the Fermi energy causing the familiar oscillations in the magnetoresistance, known as the Shubnikov-de Haas effect. This phenomenon was first used by Fowler et al,1 in the first demonstration of the existence of a two- dimensional gas of electrons bound at the surface of a (100) silicon MOSFET. The periodicity of the oscillations is directly proportional to the carrier concentration bound in the layer, and is independent of the number of layers which may be present. Since the cyclotron motion induced by the field is in the plane perpendicular to its direction, this means that a two-dimension- al system is sensitive only to the component of field parallel to the surface normal, so that rotation of the sample relative to the field can be used to provide a very simple and direct proof of the two-dimensional nature of any system under investigation.
KeywordsCarrier Concentration Landau Level Accumulation Layer Hall Voltage Hall Field
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