Magnetic Field Induced Metal-Insulator in Mercury-Cadmium Alloy and Mercury Zinc Telluride Cadmium-Telluride Superlattice
Resistivity measurements in high magnetic fields (0-12 T) and at low temperatures (1.2-30 K) on single crystal HgCdTe alloy and HgZnTe-CdTe superlattices indicate that, if the electron density is low, they exhibit a metal-insulator -transition, i.e., metallic at low magnetic field and insulating at high magnetic field. However, in heavily indium-doped alloy this is not observed. Heavily indium-doped alloys and a few unintentionally doped superlattices showed quantum oscillation (Shubnikov-de Haas oscillation) where the effective masses, Dingle temperature, and density are extracted. In low density alloys and superlattices, the analysis concluded that the transition to insulating by the bulk (three-dimensional-electron-gas) is shunted by the quasi -two-dimensional-electron gas at the buffer-layer interface or the top surface, i.e., parallel conduction. The presence of quasi-two-dimensional-electron-gas in an alloy has resulted in an anomalous behavior of the Hall coefficient with the magnetic field. The anomaly in the alloy is explained as due to the bulk three-dimensional-electron-gas exhibiting a Mott type metal-insulator-transition beyond the critical field and, eventually at high field, the quasi-two-dimensional -electron-gas becomes the dominant conducting channel. Therefore, the effective volume contributing to the charge transport is varying with the magnetic field. Similarly, in superlattices, parallel conduction is due to a few superlattice layers near the buffer-superlattice interface (or top surface) and the rest of the superlattice layers. However, in superlattices, both types of charge carriers have been found to exhibit Shubnikov-de Haas oscillations in different regimes of magnetic field. At high field only the quasi-two-dimensional -electron-gas contribute to the transport while the rest of the superlattice layers has exhibited a metal-insulator -transition at lower field.
- Pub Date:
- MERCURY ZINC TELLURIDE;
- CADMIUM ZINC TELLURIDE;
- Physics: Condensed Matter