Introduction a la theorie du transport quantique et description d'un grand nombre de resultats experimentaux. Les sujets principaux sont: l'effet Shubnikov-de Haas, la resonance cyclotron et les effets thermomagnetiques en 2 et 3 dimensions. On examine particulierement l'effet Hall quantique

Quantum transport phenomena in semiconductors in high magnetic fields

Searching for the recently predicted magnetic field induced Wigner condensation a magnetotransport anomaly was discovered in the narrow-gap semiconductors Hg08Cd02Te, PbTe, and Pb08Sn02Te In all three semiconductors a critical temperature and a critical magnetic field was found, at which a phase transition was observed to take place The anomalous behaviour is marked by a number of effects: for example by a strong increase in the longitudinal magnetoresistance, by the loss of the strong anisotropy of longitudinal and transverse magnetoresistance, and by a pronounced deviation from the magnetoresistance power-law, which is expected from the single-electron model

Experiments concerning the magnetic field induced wigner condensation in semiconductors

The energy gap of the Hg1−xCdxTe-system can be controlled by the mole fraction x of Cd. This offers the possibility to use this material as a model system for systematic investigations especially in the narrow-gap region (corresponding to 0.16 ≦ x ≦ 0.25). The electronic structure, subband occupations, subband energies, and cyclotron masses are calculated for the two-dimensional electron gas in MIS structures with this material using an approximate self-consistent method. Both, inversion and accumulation conditions are considered. Comparisons with existing limited theoretical results and with experimental ones a) show the accuracy of the method used and b) allow to interpret the detailed experimental results from Shubnikov-de Haas and cyclotron measurements available now. Predictions are made on the composition dependence of the electronic structure especially for inversion conditions.



Die Energielucke im Mischkristall Hg1−xCdxTe last sich durch die stochiometrische Zusammensetzung einstellen. Dies eroffnet die Moglichkeit systematischer Untersuchungen insbesondere im Bereich geringer Energielucken (entsprechend 0,16 ≦ x ≦ 0,25). Die elektronische Struktur, insbesondere Subbandbesetzungen, Subbandenergien und Zyklotronmassen werden fur das quasi-zweidimensionale Elektronengas in MIS-Systemen mit diesem Halbleiter berechnet. Dazu wird ein genahert selbstkonsistentes Verfahren verwendet. Es werden sowohl Inversions- als auch Akkumulationsschichten untersucht. Vergleiche mit den vorliegenden, wenigen theoretischen und mit experimentellen Resultaten zeigen a) die Genauigkeit der verwendeten Methode und erlauben b) die Interpretation des umfangreichen experimentellen Materials aus Shubnikov-de Haas- und Zyklotronresonanzuntersuchungen, das inzwischen vorliegt. Es werden Voraussagen zur Abhangigkeit der elektronischen Struktur von der stochiometrischen Zusammensetzung insbesondere fur Inversionsbedingungen gemacht.

Theory for n‐Surface Charge Layers in Hg1−xCdxTe MIS Structures

Dreidimensionaler Wigner-Kristall?

This paper will review theoretical work on magnetic-field-induced Wigner condensation of three-dimensional electron systems in semiconductors and discuss some closely related work on two-dimensional systems.

Theoretical Aspects of Wigner Condensation

Some narrow‐gap mixed crystal semiconductors show a magnetic field induced transport anomaly at low temperatures. The anomaly is accompanied by a transition from a low to a high resistivity state, which in turn causes a strongly nonlinear I‐V characteristic. We have investigated microwave mixing near such a phase transition in n‐type Hg0.8Cd0.2Te with a frequency of 37 GHz at 1.5 K and in magnetic fields up to 8.5 T. The sensitivity characteristic was measured and the responsivity determined to be about 15 times higher than that of a hot‐carrier InSb bolometer. The time resolution of this new bolometer (=10−7 s) was slightly better than in InSb.

B. Schlicht

Papers

A new sensitive microwave bolometer heterodyne receiver