Electron transport through and in quantum dot arrays

Abstract

The present thesis investigates serial quantum dot arrays of different sizes, the double quantum dot, the triple quantum dot, and the quadruple quantum dot. The quantum dot device is based on a two-dimensional electron gas formed in a GaAs/AlGaAs heterostructure. A quantum point contact in the vicinity of the quantum dots is utilized as a charge sensor, allowing to detect tunneling of single electrons into or out of the quantum dots as well as between two of the quantum dots. Two qualitatively different regimes are discussed, the transport regime and the isolated regime.

In the transport regime, where the quantum dots are well coupled to electron reservoirs on both sides, electrons can tunnel from one reservoir to the other through the array. Gate voltage dependent measurements are used to characterize the transport properties through the quantum dot arrays and to extract electrostatic properties. For all array sizes, long-range transport across quantum dots in Coulomb blockade is observed for the strong coupling regime.

The isolated regime is reached by increasing the tunnel barriers between reservoirs and the quantum dot array on both sides until tunneling from and into the reservoirs is fully suppressed within the measurement timescales. The number of electrons in an isolated array is fixed, but electrons can still be redistributed inside the array. The charge reconfiguration inside the arrays is tracked using the charge detector. A high level of control over the coupling, and thus the interdot transitions, including long-range transitions between non-neighboring quantum dots, is demonstrated. Time-resolved charge detection was used to investigate the tunneling dynamics of a single, two, and three electrons loaded into a double quantum dot, where the three electron case shows a high sensitivity to environmental parameters.