Formation of quantum dots in the potential fluctuations of InGaAs heterostructures probed by scanning gate microscopy

TL;DR

This study uses scanning gate microscopy to reveal how local potential fluctuations in InGaAs heterostructures lead to quantum dot formation, causing conductance oscillations linked to Coulomb blockade effects.

Contribution

It provides direct experimental evidence of quantum dot formation due to disorder-induced potential fluctuations in InGaAs heterostructures, supported by electrostatic simulations.

Findings

Conductance oscillations are periodic in tip voltage.

Oscillations form concentric circles increasing with negative tip voltage.

Quantum dots form at potential fluctuation sites, causing Coulomb blockade.

Abstract

The disordered potential landscape in an InGaAs/InAlAs two-dimensional electron gas patterned into narrow wires is investigated by means of scanning gate microscopy. It is found that scanning a negatively charged tip above particular sites of the wires produces conductance oscillations that are periodic in the tip voltage. These oscillations take the shape of concentric circles whose number and diameter increase for more negative tip voltages until full depletion occurs in the probed region. These observations cannot be explained by charging events in material traps, but are consistent with Coulomb blockade in quantum dots forming when the potential fluctuations are raised locally at the Fermi level by the gating action of the tip. This interpretation is supported by simple electrostatic simulations in the case of a disorder potential induced by ionized dopants. This work represents a local investigation of the mechanisms responsible for the disorder-induced metal-to-insulator transition observed in macroscopic two-dimensional electron systems at low enough density.