Résumé
By experiments under hydrostatic pressure (up to 13 Kbar) in high magnetic fields (0–20T) we investigate the role of Si donors of GaAlAs in the quantum and ultraquantum transport regimes of quasi-2D electrons gas of GaAs-GaAlAs heterojunctions with a spacer. In the ultraquantum regime we analyse the metal-nonmetal transition and magnetic freeze-out due to bound donor states as a function of the spacer thickness and of the 2D electron density N. In the quantum regime (Quantum Hall Effect) we show the role of these Si donors in the localization phenomenon and study it when the spacer width and NS vary.
In both investigated regimes we point out that the screening of the Coulomb interaction between 2D electrons and donors is essential to account for the experiments.