Quantum wells,Quantum wires and Quantum
Presented By_ To_
Sanjeeb Limbu(Reg.No:14305019) Dr.A.Subramania Sir
M.Tech.-Nanoscience & Technology Associate Professor(CNST)
When the size or dimension of a material is continuously reduced
from a large or macroscopic size, such as meter or centimetre to a
very small size, the properties remain the same at first then small
change begin to occur, until finally when the size drops below 100
nm. In this way formed a new structure of the material is called
nanostructure. The wells, wires and dots are nothing but
nanostructure of the material. The nanostructure are explain
through the quantum mechanics so is called quantum wells,
quantum wires and quantum dots. Its not a classical wells, wires and
dots. Its also called low dimensional structure.
Classification of law dimensional materials
1.Three dimensional (3D) structure or bulk structure: No
quantisation of the particle motion occurs i.e., the particle is free. Electron in
conduction band and holes in valence band are free to move in all three
dimensions of space. Eg.cube
2.Two-dimensional (2D) structure or quantum well:
Quantum confinement in nanostructure-Ifone dimension is confined or reduced
to the nanometre ranges while other two dimensions remain large then we get a
structurecalled quantum well. Eg.nano wires,nanorod,nanotube.
Electrons confined in one direction
Quantum wells (Thin films) : Electrons
can easily move in 2 dimensions
(One dimensional quantisation)
3.One-dimensional (1D) structure or quantum wire: If two
dimensions are reduced in to the nanometre range and remain large the structure
to as a quantum wire. Eg.nanoseed (Graphene)
Electron confined in 2 dimensions
Quantum wires: Electron can freely
easily move in 1 dimension. (2 dimensional quantisation)
The semiconductor wires surrounded by a material with large
band gap .Surrounding material confines electron and hole in
two dimensions(carrierscan only move in one dimensions) due
its larger bandgap.Radius of quantum wires,nanorods and nano
tube, nano pillars (1D structures)1-100 nm range (Typical nano-
4.Zero-dimensional (0D) structure or quantum dot: The
extreme case of this process of size reduction in which all three dimensions reach
the low nanometre range is called a quantum dot. Eg. Nano dot
Electron confined in three dimensions
Quantum dot: electron can easily moves
in zero dimensions.
(3 dimensional quantisation)
Electron and holes are confined in all the
three dimensions of space by a surrounding
material with a larger band gap
Discrete energy levels(artificial atoms)
No quantum dots has a larger band gap
like bulk semiconductor.
Typical dimensions: 1-10 nm
Comparison of Nanostructure:
Progressive generation of rectangular nanostructures.
Progressive generation of curvilinear nanostructures.
Density of states: The density of states of a system describes the
number of states per interval of energy of each energy level that are available
to be occupied by electrons. Density of states moving from the bulk(3D) crystal
to a quantum well(2D) ,there is a further change in the density of on moving
quantum wires(1D) and quantum dots(0D),
Structure Degree of
Bulk Material 0D
Quantum Well 1D 1
Quantum Wire 2D
Quantum Dot 3D d(E)
Quantum wells are formed in semiconductors by having a material,
like gallium arsenide sandwiched between two layers of a material with a
wider band gap, like aluminium arsenide. (Other example: layer of indium
gallium nitride sandwiched between two layers of gallium nitride ) These
structures can be grown by molecular beam epitaxy or chemical vapor
deposition with control of the layer thickness down to monolayer's.
How to prepare a quantum well ???
Application of quantum wells:
In optical devices such as laser diodes .Formed by semiconductor
materials quartz and silica(Absorb/Emit light)efficiently).
They are also used to make HEMTs (High Electron Mobility
Transistors), which are used in low-noise
Quantum well infrared photo detectors are also based on
quantum wells, and are used for infrared imaging (Absorb
How to prepare a quantum wire ???
a) The most important application of nanowires in nanoelectronics is using them
as junctions or as multi-segment nanowires or crossed nanodevices.
b) Quantum wire is used in energy storagedevices