Imaging a Coupled Quantum Dot - Quantum Point Contact System

TL;DR

This study uses a scanning force microscope to investigate charge dynamics in a coupled quantum dot and quantum point contact system, revealing charge traps and their impact on electron behavior.

Contribution

It introduces a method to distinguish charge traps from quantum dot charging events and analyzes the trap-induced potential and interactions.

Findings

Charge traps are below 0.1% of doping density.

Trap interaction energy is significant relative to dot's charging energy.

Charge traps may cause parametric charge rearrangements.

Abstract

We performed measurements on a quantum dot and a capacitively coupled quantum point contact by using the sharp metallic tip of a low-temperature scanning force microscope as a scanned gate. The quantum point contact served as a detector for charges on the dot or nearby. It allowed us to distinguish single electron charging events in several charge traps from charging events on the dot. We analyzed the tip-induced potential quantitatively and found its shape to be independent of the voltage applied to the tip within a certain range of parameters. We estimate that the trap density is below 0.1% of the doping density and that the interaction energy between the quantum dot and a trap is a significant portion of the dot's charging energy. Possibly, such charge traps are the reason for frequently observed parametric charge rearrangements.