A wetting layer is an monolayer of
atom
Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons.
Every solid, liquid, gas ...
s that is
epitaxially grown on a flat surface. The atoms forming the wetting layer can be semimetallic elements/compounds or metallic alloys (for thin films). Wetting layers form when depositing a lattice-mismatched material on a crystalline substrate. This article refers to the wetting layer connected to the growth of self-assembled quantum dots (e.g.
InAs
Indium arsenide, InAs, or indium monoarsenide, is a narrow-bandgap semiconductor composed of indium and arsenic. It has the appearance of grey cubic crystals with a melting point of 942 °C.
Indium arsenide is similar in properties to galliu ...
on
GaAs
Gallium arsenide (GaAs) is a III-V direct band gap semiconductor with a zinc blende crystal structure.
Gallium arsenide is used in the manufacture of devices such as microwave frequency integrated circuits, monolithic microwave integrated ...
). These
quantum dots
Quantum dots (QDs) are semiconductor particles a few nanometres in size, having optical and electronic properties that differ from those of larger particles as a result of quantum mechanics. They are a central topic in nanotechnology. When the ...
form on top of the wetting layer. The wetting layer can influence the states of the quantum dot for applications in
quantum information
Quantum information is the information of the state of a quantum system. It is the basic entity of study in quantum information theory, and can be manipulated using quantum information processing techniques. Quantum information refers to both t ...
processing and
quantum computation
Quantum computing is a type of computation whose operations can harness the phenomena of quantum mechanics, such as superposition, interference, and entanglement. Devices that perform quantum computations are known as quantum computers. Thoug ...
.
Process
The wetting layer is epitaxially grown on a surface using
molecular beam epitaxy
Molecular-beam epitaxy (MBE) is an epitaxy method for thin-film deposition of single crystals. MBE is widely used in the manufacture of semiconductor devices, including transistors, and it is considered one of the fundamental tools for the devel ...
(MBE). The temperatures required for wetting layer growth typically range from 400-500 degrees
Celsius. When a material ''A'' is deposited on a surface of a lattice-mismatched material ''B'', the first atomic layer of material ''A'' often adopts the lattice constant of ''B''. This mono-layer of material ''A'' is called the wetting layer. When the thickness of layer ''A'' increases further, it becomes energetically unfavorable for material ''A'' to keep the lattice constant of ''B''. Due to the high strain of layer ''A'', additional atoms group together once a certain critical thickness of layer ''A'' is reached. This island formation reduces the
elastic energy
Elastic energy is the mechanical potential energy stored in the configuration of a material or physical system as it is subjected to elastic deformation by work performed upon it. Elastic energy occurs when objects are impermanently compressed, ...
.
Overgrown with material ''B'', the wetting layer forms a
quantum well
A quantum well is a potential well with only discrete energy values.
The classic model used to demonstrate a quantum well is to confine particles, which were initially free to move in three dimensions, to two dimensions, by forcing them to occup ...
in case material ''A'' has a lower
bandgap
In solid-state physics, a band gap, also called an energy gap, is an energy range in a solid where no electronic states can exist. In graphs of the electronic band structure of solids, the band gap generally refers to the energy difference ( ...
than ''B''. In this case, the formed islands are
quantum dots
Quantum dots (QDs) are semiconductor particles a few nanometres in size, having optical and electronic properties that differ from those of larger particles as a result of quantum mechanics. They are a central topic in nanotechnology. When the ...
. Further
annealing can be used to modify the physical properties of the wetting layer/
quantum dot
Quantum dots (QDs) are semiconductor particles a few nanometres in size, having optical and electronic properties that differ from those of larger particles as a result of quantum mechanics. They are a central topic in nanotechnology. When the q ...
.
Properties
The wetting layer is a close-to mono-atomic layer with a thickness of typically 0.5
nanometer
330px, Different lengths as in respect to the molecular scale.
The nanometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: nm) or nanometer (American and British English spelling differences#-re, ...
s. The electronic properties of the
quantum dot
Quantum dots (QDs) are semiconductor particles a few nanometres in size, having optical and electronic properties that differ from those of larger particles as a result of quantum mechanics. They are a central topic in nanotechnology. When the q ...
can change as a result of the wetting layer.
[
][
] Also, the
strain of the
quantum dot
Quantum dots (QDs) are semiconductor particles a few nanometres in size, having optical and electronic properties that differ from those of larger particles as a result of quantum mechanics. They are a central topic in nanotechnology. When the q ...
can change due to the wetting layer.
[
]
Notes
External links
Wetting layer on arxiv.orggroup website of M. Dähne
{{Semiconductor laser
Quantum electronics
Thin film deposition