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Etching of zinc blende InAs nanowires for quantum dot studies

Mkolongo, Chris LU (2025) PHYM03 20251
Solid State Physics
Department of Physics
Abstract
We explored various methods for inducing quantum dots (QDs) in pure zinc blende (ZB) InAs nanowires. This material exhibits high conductivity due to the presence of an intrinsic accumulation layer of charge carriers, resulting from surface band bending and donor impurities. To create regions that can be depleted by gate potentials (barriers) in the axial direction of the nanowire, we employed both dry and wet etching techniques. For dry etching, we used an argon milling process with a milling rate of ∼ 0.52 nm/s, while the wet etching method involved a solution of diluted citric acid and hydrogen peroxide, which had an etch rate of ∼ 1.3 nm/s. Subsequently, we performed electrical characterization of the devices fabricated using these... (More)
We explored various methods for inducing quantum dots (QDs) in pure zinc blende (ZB) InAs nanowires. This material exhibits high conductivity due to the presence of an intrinsic accumulation layer of charge carriers, resulting from surface band bending and donor impurities. To create regions that can be depleted by gate potentials (barriers) in the axial direction of the nanowire, we employed both dry and wet etching techniques. For dry etching, we used an argon milling process with a milling rate of ∼ 0.52 nm/s, while the wet etching method involved a solution of diluted citric acid and hydrogen peroxide, which had an etch rate of ∼ 1.3 nm/s. Subsequently, we performed electrical characterization of the devices fabricated using these methods in a dilution refrigerator at a base temperature of 20 mK. We found that most of these devices did not yield desirable results due to limitations imposed by the fabrication methods employed. Argon-milled devices showed significant charge fluctuation (noise), likely due to surface defects that altered the electrostatic environment of the QDs. In contrast, wet-etching was not sufficiently localized due to its diffusive and isotropic nature.

Additionally, the project explored methods to increase charging energy and quantum confinement on epitaxially grown QDs. Using the previously developed wet etching method, the epitaxial QDs were etched radially. As a result, these QDs required less negative back gate voltage to achieve complete electron depletion due to reduced screening effect. The charging energy of the QDs in the few-electrons regime increased due to increased confinement. Finally, the etched QDs were subjected to external magnetic fields to study the Zeeman effect, from which effective g−factors (g∗) were extracted. The magnetic field was applied parallel and orthogonal to the nanowire. The g∗−factors were ∼ 8.9 and ∼ 10 for B-fields parallel and orthogonal to the nanowire axial direction, respectively, thus showing no sign of strong quenching. (Less)
Popular Abstract
Fabrication of zero-dimensional devices and manipulation of current flow

Electricity is one of the most significant resources that profoundly impacts our daily lives. We all know that to transport electrical power from one place to another, we need cables and wires. The electric current flowing through the three-dimensional cables obeys the laws of classical physics laid out by various scientists such as Georg Ohm and Alessandro Volta in the 19th century. But what happens when the current needs to pass
through a material with spatial dimensions reduced to zero (a dot), such that electrons can go through it one-by-one? Are there new physical laws that govern the flow of current? Is it even possible to have a zero-dimensional conductor?
... (More)
Fabrication of zero-dimensional devices and manipulation of current flow

Electricity is one of the most significant resources that profoundly impacts our daily lives. We all know that to transport electrical power from one place to another, we need cables and wires. The electric current flowing through the three-dimensional cables obeys the laws of classical physics laid out by various scientists such as Georg Ohm and Alessandro Volta in the 19th century. But what happens when the current needs to pass
through a material with spatial dimensions reduced to zero (a dot), such that electrons can go through it one-by-one? Are there new physical laws that govern the flow of current? Is it even possible to have a zero-dimensional conductor?

Low-dimensional structures can be produced in a controlled laboratory environment. One-dimensional semiconductors, commonly referred to as nanowires, can be grown by chemically balancing different elements such as indium, gallium, arsenic, and many others. Nanowires can grow up to tens of micrometers in length while having a diameter of a few nanometers. Thanks to their high aspect ratio, nanowires provide an ideal platform for creating zero-dimensional structures, also known as quantum dots (QDs). As one can tell from the name, the laws of classical physics are not the only governing laws, but a new/different type of physics emerges, quantum physics.

QDs in nanowires serve as a medium for studying novel quantum
physics as well as for engineering applications. QDs can be used as charge sensors to detect changes in the surrounding electrostatic environment, enabling applications in quantum computation, thermometry, and other fields. The size of the QD plays a crucial role in defining its electrical properties. Smaller QDs are less prone to charge fluctuations and exhibit more
pronounced quantum mechanical effects, such as the discretization of the energy spectrum. This can hinder electron flow to the rest of the nanowire unless one of the discrete energy states acts as a stepping stone for electrons. An analogy would be an elevator in a building. Suppose you are an electron on the top floor and want to go to a lower floor. In that case, the elevator (energy level in QD) acts as a bridge between the two floors (electron reservoirs).

One of the many notable semiconductors grown in laboratories is indium arsenide (InAs) nanowires, which are known to have high charge carrier concentrations. While this is a beneficial property in many cases, it poses a challenge in creating QDs in such a carrier-rich environment. In this work, we investigated various etching methods to form QDs in InAs nanowires, as well as a technique to reduce the size of crystal-phase-defined QDs through etching. One of the etching methods used was dry etching, in which energetic argon ions strike the surface of the nanowire. This method is commonly referred to as argon milling. The second method
was wet etching, in which nanowires were immersed in liquid chemicals. QDs formed from different crystal phases were reduced in size through the radial wet etching of the nanowires. (Less)
Please use this url to cite or link to this publication:
author
Mkolongo, Chris LU
supervisor
organization
course
PHYM03 20251
year
type
H2 - Master's Degree (Two Years)
subject
keywords
Wet etching, argon milling, zinc blende (ZB) nanowire, InAs nanowires, Coulomb blockade, quantum dots, double quantum dots, few-electron regime, many-electron regime, tunnel barrier symmetry, Zeeman spin-splitting, effective g-factor, g-factor quenching, etched quantum dots
language
English
id
9212021
date added to LUP
2025-09-24 13:54:18
date last changed
2025-09-24 13:54:18
@misc{9212021,
  abstract     = {{We explored various methods for inducing quantum dots (QDs) in pure zinc blende (ZB) InAs nanowires. This material exhibits high conductivity due to the presence of an intrinsic accumulation layer of charge carriers, resulting from surface band bending and donor impurities. To create regions that can be depleted by gate potentials (barriers) in the axial direction of the nanowire, we employed both dry and wet etching techniques. For dry etching, we used an argon milling process with a milling rate of ∼ 0.52 nm/s, while the wet etching method involved a solution of diluted citric acid and hydrogen peroxide, which had an etch rate of ∼ 1.3 nm/s. Subsequently, we performed electrical characterization of the devices fabricated using these methods in a dilution refrigerator at a base temperature of 20 mK. We found that most of these devices did not yield desirable results due to limitations imposed by the fabrication methods employed. Argon-milled devices showed significant charge fluctuation (noise), likely due to surface defects that altered the electrostatic environment of the QDs. In contrast, wet-etching was not sufficiently localized due to its diffusive and isotropic nature.

Additionally, the project explored methods to increase charging energy and quantum confinement on epitaxially grown QDs. Using the previously developed wet etching method, the epitaxial QDs were etched radially. As a result, these QDs required less negative back gate voltage to achieve complete electron depletion due to reduced screening effect. The charging energy of the QDs in the few-electrons regime increased due to increased confinement. Finally, the etched QDs were subjected to external magnetic fields to study the Zeeman effect, from which effective g−factors (g∗) were extracted. The magnetic field was applied parallel and orthogonal to the nanowire. The g∗−factors were ∼ 8.9 and ∼ 10 for B-fields parallel and orthogonal to the nanowire axial direction, respectively, thus showing no sign of strong quenching.}},
  author       = {{Mkolongo, Chris}},
  language     = {{eng}},
  note         = {{Student Paper}},
  title        = {{Etching of zinc blende InAs nanowires for quantum dot studies}},
  year         = {{2025}},
}