Nanotechnology in Semiconductor Nanostructure. Presentation on "Quantum Dot", was performed under the Subject "QUANTUM PHENOMENA IN NANOSTRUCTURES" at AIUB. The simulation is done from a website nanoHUB which stands for online simulation for nanotechnology- https://nanohub.org/

1. American International University- Bangladesh
(AIUB)
(School of Engineering)
Presenter
Nusrat Irin Chowdhury Mary
QUANTUM DOT

2. Quantum
 Quantum is the Latin word for amount, meaning the
smallest possible discrete unit of any physical
property, such as energy or matter.
 Max Planck used it in a presentation to the German
Physical Society. Planck wrote a mathematical
equation involving a figure to represent individual
units of energy. He called the units as quanta .
 Quantum is sometimes used loosely, in an adjectival
form, to mean on such an infinitesimal level as to be
infinite, as, for example, you might say "Waiting for
pages to load is quantumly boring."

3. What are Quantum Dots?
 Quantum dots are semi-
conductors that are on the
nanometer scale.
 Obey quantum mechanical
principle of quantum
confinement.
 Exhibit energy band gap
that determines required
wavelength of radiation
absorption and emission
spectra.
 Requisite absorption and
resultant emission
wavelengths dependent on
dot size.
Figure: Schematic plot of the single
particle energy band gap. The upper
parabolic band is the conduction
band, the lower the valence.

4. Quantum Dots Description
The name “dot” suggests
an extremely small region
of space. The number of
free electrons in the dot
can be very small.
The deBroglie
wavelength of these
electrons is comparable
to the size of the dot, and
the electrons occupy
discrete quantum levels
and have a discrete
excitation spectrum.
Figure: Band gap energy of
quantum dots vary with its
size.

5. Quantum Dots Description contd.
Cadmium Mercury
Telluride (CdHgTe),
Cadmium Selenide
(CdSe), Cadmium
Selenide/Zinc
Sulfide (CdSe/ZnS),
Cadmium Sulfide
(CdS), Cadmium
Telluride (CdTe),
Cadmium
Telluride/Cadmium
Sulfide (CdTe/CdS),
Lead Selenide
(PbSe), Lead
Sulfide (PbS)

6. Figure: The
energy band gap
associated with
semi-conducting
materials. In
order to produce
electric current
electrons must
exist in the
conduction band.
Energy Bands in Quantum Dots

7. Confinement - Infinite Square Well
Potential
Figure: Quantized energy levels of a particle in a box.

8. Figure: Solutions of quantum
dots of varying size. The
variation in color of each
solution illustrating the particle
size dependence of the optical
absorption for each sample.
The smaller particles are in the
blue solution (absorbs blue),
and that the larger ones are in
the red (absorbs red).
Solutions of Quantum Dots

9. Characteristics of Quantum Dot
 An electron in a quantum dot will act more like an electron
in a molecule than an electron in a bulk solid, and for this
reason, quantum dots are sometimes called artificial
molecules.
 The charging energy of QD is analogous to the ionization
energy of an atom. This is the energy required to add or
remove a single electron from the dot. Measuring their
transport properties, i.e., by their ability to carry an electric
current, quantum dots are artificial atoms with the
intriguing possibility of attaching current and voltage leads
to probe their atomic states.

10. Application of Quantum Dot
 Special Quantum Dots could Improve Transparent
Solar Cells
 Shiny quantum dots brighten future of solar cells
 Quantum dot TVs to be launched by mid-2014
 Quantum Materials Now Shipping Size-Optimized
Metallic Oxide
 Quantum dots can charge your Smartphone in 30
seconds

11. Solar Cells and Photovoltaic
 Traditional solar cells are made of semi-conductors and
expensive to produce. Theoretical upper limit is 33%
efficiency for conversion of sunlight to electricity for
these cells.
 Utilizing quantum dots allows realization of third-
generation solar cells at ~60% efficiency in electricity
production while being low cost per square meter of
paneling necessary.
 Effective due to quantum dots’ ability to preferentially
absorb and emit radiation that results in optimal
generation of electric current and voltage.

12. Medical Imaging and Disease
Detection
 Can be set to any arbitrary emission spectra to allow labeling
and observation of detailed biological processes.
 Useful tool for monitoring cancerous cells and providing a
means to better understand its evolution.
 In future, could also be armed with tumor-fighting toxic
therapies to provide the diagnosis and treatment of cancer.
 Resistant to degradation than other optical imaging probes
such as organic dyes, allowing them to track cell processes
for longer periods of time.
 Offer a wide broadband absorption spectrum while
maintaining a distinct, static emission wavelength.

13. Other Future Quantum Dot
Applications
 Anti-counterfeiting capabilities: inject dots into liquid
mixtures, fabrics, polymer matrices, etc. Ability to
specifically control absorption and emission spectra to
produce unique validation signatures. Almost
impossible to mimic with traditional semi-conductors.
 Counter-espionage / Defense applications: Integrate
quantum dots into dust that tracks enemies. Protection
against friendly-fire events.
 Research continues. The possibilities seem endless…

14. Quantum Dot in nanoHUB
 There are two input
methods:
1. Device Structure
2. Light Source
The Figure shows the
view of the tool
In simulation part the used tool is “Quantum Dot Lab”
under “artificial atom” tag.

15. Quantum Dot Lab in nanoHUB contd.
Device Structure quantify the physical structure of the QD. It consist
of the following parameters:
a. Number of states it will be having (with corresponding valid numbers
with unit of nm)
b. Surface Passivation
c. physical size (cuboid, cylinder, dime, pyramid, spheroid)
d. dimensions (in x-, y-, z- directions with maximum values of 20nm the
unit of nm)
e. effective mass (as an ex two values are given, the possible values
are 0.005 to 3.0)
f. discretization (with the unit of nm)
g. energy gap (between 0eV to 20eV with the unit of J or eV)
The Light Source signify if any light source is fall on to the Quantum
Dots. This input is also having some parameters like device structure
has

16. Quantum Dot Lab in nanoHUB contd.
Parameter- a
Number of
states the
simulation
will be
having, which
follow some
values from 1
to 150.

17. Quantum Dot Lab in nanoHUB contd.
Parameter- b
Surface
Passivation-
Which deals
with wave
function. It
can be turn
on/off. If
unchecked
means
wavefunction
‘0’ outside

18. Quantum Dot Lab in nanoHUB contd.
Parameter- c
Geometry,
which means
for physical
size, whether
its cubic or
cylinder,
dime, pyramid
or spheroid.

19. Quantum Dot Lab in nanoHUB contd.
Parameter- d
dimensions
(in x-, y-, z-
directions with
maximum
value ranges
with the unit
of nm). The
other
parameter’s
values were
set according
to them.

20. Quantum Dot Lab in nanoHUB contd.
Under the
“Light Source”
tab some
parameter is
there. Which
will also
having some
respective
angle and
values and
was set
according to
them.

21. Quantum Dot Lab in nanoHUB contd.
After given with
the appropriate
inputs, the
simulation is
done. It will give
graphical
representations
with the
“Result” window
presenting
outputs.

22. Quantum Dot Lab in nanoHUB contd.
 The first result is the “3D Wavefunction”

23. Quantum Dot Lab in nanoHUB contd.
 The second result is the “Energy states”

24. Quantum Dot Lab in nanoHUB contd.
 The third result is “Light and dark transition (X- polarized)”

25. Quantum Dot Lab in nanoHUB contd.
 The third result is “Light and dark transition (Y-polarized)”

26. Quantum Dot Lab in nanoHUB contd.
 The third result is “Light and dark transition (Z-polarized)”

27. Quantum Dot Lab in nanoHUB contd.
 The next is “Light and dark transition (phi= 0, theta=
45)” which is in a spherical coordinate system.

28. Quantum Dot Lab in nanoHUB contd.
 The “Absorption (phi= 0, theta= 45)”

29. Quantum Dot Lab in nanoHUB contd.
 The “Absorption sweep of angle theta”

30. Quantum Dot Lab in nanoHUB contd.
The last two results are “Input deck” & “Output log” which are
representing inputs to the simulation and database information
corresponding the inputs given to the running tool.