Suppression of the virtual Anderson transition in a narrow impurity band of doped quantum well structures

TL;DR

This paper investigates how extrinsic compensation and impurity concentration affect the virtual Anderson transition in doped quantum well structures, revealing suppression mechanisms and the transition to metallic behavior at high doping levels.

Contribution

It provides new insights into how compensation and impurity levels influence the Anderson transition and the onset of metallic conductivity in quantum wells.

Findings

Strong compensation suppresses the Anderson transition due to increased disorder.

Higher dopant concentration initially suppresses the transition but eventually leads to metallic conductivity.

The transition is affected by the overlap of Hubbard bands and Mott transition at high doping.

Abstract

Earlier we reported an observation at low temperatures of activation conductivity with small activation energies in strongly doped uncompensated layers of p-GaAs/AlGaAs quantum wells. We attributed it to Anderson delocalization of electronic states in the vicinity of the maximum of the narrow impurity band. A possibility of such delocalization at relatively small impurity concentration is related to the small width of the impurity band characterized by weak disorder. In this case the carriers were activated from the "bandtail" while its presence was related to weak background compensation. Here we study an effect of the extrinsic compensation and of the impurity concentration on this "virtual" Anderson transition. It was shown that an increase of compensation initially does not affect the Anderson transition, however at strong compensations the transition is suppressed due to increase of disorder. In its turn, an increase of the dopant concentration initially leads to a suppression of the transition due an increase of disorder, the latter resulting from a partial overlap of the Hubbard bands. However at larger concentration the conductivity becomes to be metallic due to Mott transition.