Transport through quantum dot systems

Quantum dots are artificial systems in which charge carriers are spatially confined to the order of their Fermi wavelength. Due to this confinement quantum dots exhibit a discrete energetic spectrum. Coulomb repulsion and Pauli exclusion hereby prevent the energetic states to be occupied by more the one charge carrier at a time.

The focus of this project lies on the investigation of quantum dot arrays based on two-dimensional electron gases (2DEGs) which are formed in GaAs/AlGaAs heterostructures. Metallic Schottky gates are fabricated on the surface of the heterostructure via electron beam lithography and by applying negative potentials to these gates, the 2DEG below can be depleted to define the quantum dots. In the same way a quantum point contact (QPC) is defined in the vicinity of the quantum dots and acts as a highly sensitive charge detector.

This QPC charge sensor allows the real-time tracking of electrons moving through or inside a quantum dot system and opens up opportunities like implementing a feedback protocol to suppress the shot noise in a single electron transistor device [1].

False color SEM image of a quadruple quantum dot device. The quantum dots are depicted as green circles. Red arrows indicate the possibility to move electrons through the array. This movement can be tracked by the QPC charge sensor, depicted by the blue arrow.

[1] T. Wagner; P. Strasberg; J. C. Bayer; E. P. Rugeramigabo; T. Brandes; R. J. Haug, Strong suppression of shot noise in a feedback-controlled single-electron transistor, Nature Nanotechnology DOI:10.1038/nnano.2016.225 (2016).