Chapter 11 - Electronic transport properties of quantum dots

Abstract

This chapter presents both the basic theory and the experimental data for the electron spectroscopy as a function of magnetic field and temperature for two vertical quantum dot systems—the fabricated quantum dot and the impurity quantum dot. In a fabricated quantum dot, the potential an electron experiences along the z direction is due to the semiconductor heterostructure band alignments and is modeled as a finite square well potential as in a quantum well. The potential the electron experiences along the lateral (x-y) directions depends critically on the highly anisotropic reactive ion etching process. If the lateral shape of the dot is asymmetric, each eigenstate of the system is, in general, nondegenerate. If the dot has cylindrical symmetry, the various eigenstates reflect that symmetry. An additional effect to be considered is the Fermi-level pinning of the exposed side walls of the device. The Fermi level in the exposed semiconductor material gets pinned at a fixed value near the midgap. The binding energy of an impurity in a quantum well depends on the properties of the well, in particular, its width L and its barrier height V0. The impurity binding energy increases as the well width decreases as long as the penetration of the quantum well wave function [x(z)] in the barriers remains small.