A. De Keyser

Magnetotransport properties of Si-δ-doped InSb layers grown on GaAs

Abstract Magnetotransport measurements up to 50 T have been performed on single Si-δ-doped layers in InSb as well as on a structure consisting of 10 δ-doped layers which are situated 50 nm apart. The low resistivity 3D channel that conceals the 2D conduction at low magnetic fields for the single δ-layers is not observed in the 10 δ-layer configuration. The occurrence of a quantum Hall plateau at a filling factor v = 1 in this system implies that the 2D conduction is due to a single 2D electron gas rather than to 10 independent 2D channels.

Pulsed critical current measurements of NbTi in perpendicular and parallel pulsed magnetic fields using the new Cryo-BI-Pulse System

Rapid transport current versus high magnetic field characterisation of high-irreversibility type II superconductors is important to maximise their critical parameters. HTS conductors are already used to produce insert coils that increase the fields of conventional magnets made from NbTi, (Nb, Ta)3Sn and Nb3Al wires. There is fundamental interest in the study of HTS tapes and wires in magnetic fields higher than 21T, the current limit of superconducting magnets producing a DC field. Such fields can be obtained by using pulse techniques. High critical currents cannot be routinely measured with a continuous current applied at liquid helium, hydrogen or neon temperatures because of thermal and mechanical effects. A newly developed pulsed magnetic field and pulsed current system which allows rapid Jc(B, T) measurements of the whole range of superconducting materials was tested with a multifilamentary NbTi wire in perpendicular and parallel orientations.

Cyclotron resonance of 2D electrons at Si-δ-doped InSb layers grown on GaAs

Abstract Cyclotron resonance (CR) of the electrons accumulated at sheets with heavy Si doping in InSb were observed using far infrared radiation. The angular dependence of the CR follows closely the 1/cos θ behaviour with some small deviations at high angles attributed to coupling between subbands. From the effective mass of the lowest subband, which is found to be 0.027 m 0 , the bottom of the lowest subband was determined to lie 125 meV below the Fermi level.

Interplay of 2D and 3D charge carriers in Si-δ-doped InSb layers grown epitaxially on GaAs

Abstract Magnetotransport experiments on Si-δ-doped layers in InSb have revealed the presence of a two-dimensional as well as a three-dimensional conduction channel in these structures. A theoretical description of the interplay between two-dimensional and three-dimensional charge carriers is given, taking into account magnetic freeze-out of the three-dimensional electrons and the quantization of electron motion in the two-dimensional electron gas. The nature of the single 2DEG that has been observed in a structure consisting of 10 δ-layers separated by 50 nm of InSb is investigated by depopulation experiments and by additional experiments on bulk InSb layers grown on GaAs.

Size effects in the transport properties of thin Sc1−xErxAs epitaxial layers buried in GaAs

Abstract Size effects have been studied in the transport properties of Sc 1− x Er x As layers with thicknesses ranging from 20 to 0.8 nm. Shubnikov-de Haas (SdH) measurements in tilted magnetic fields confirm the confinement of charge carriers in the Sc 1− x Er x As quantum wells. For the layers with thickness less than 5.7 nm, the magnetoresistance is increasingly negative for decreasing thickness. Different size mechanisms which may be responsible for the observed behaviour are discussed.