This document summarizes a graduation project report on using the NEMO 5 simulation tool to model the energy states and wavefunctions of a gallium arsenide quantum dot nanostructure. Key findings include: 1) NEMO 5 was used to successfully model an 11nm x 11.5nm x 5nm GaAs quantum dot and obtain its energy bands and electron wavefunctions. 2) Computer simulations are important for designing nanostructures before fabrication to reduce costs. 3) Future work includes using NEMO 5 to model more complex structures and exploring other simulation tools through the NanoHub website.

1. Al-Nahrain University
College of Science
Department of Physics
Computer Simulation of
Nano-Structures
(Graduation Project Report Submitted to the Department
of Physics, College of Science, Al-Nahrain)
By
Akeel Abdul-Ridha Khudhayir
Supervised by
Dr. Mohammed A. Z. Habeeb
(April, 2015)

2. Outline:
Review & History.₪
Quantum Dots (QDs).₪
Application of Quantum Dots.₪
Computations in Nanoscience.₪
NEMO 5 Simulation Tool.₪
Definition of the Problem.₪
Computations & Results.₪
Conclusions.₪
Future Work.₪

3. Nanoscience:Ascienceof lowdimensionalstructures.
Review & History
Feynman’s thesis at
1959; “there’s plenty of
room at the bottom”.

4. Quantum Dots(QDs)
Quantum Confinement in QDs: All carriers
acts as free carriers in all 3-Dimensions.
◊ Artificial atoms confined in 3-D.

5. Applications of Quantum Dots
Organic dyes◊
Some of them are:
In vivo imaging of biological
specimens.
Cellular labeling & ill detection.

6. ◊ Solar cell fabrication: Quantum dots have been
found to emit up to three electrons per photon
of sunlight, as opposed to only one for standard
photovoltaic panels.

7. Computations in Nanoscience
Effective mass theory :
( A single electron in the conduction
band will behave like a free electron
but with an effective mass ) .
- As an example, in the GaAs, the
conduction band effective mass m* of
free electrons is 0.067 of its mass me .

8. There are computer programs &
tools to simulate the nano-
structures, some them are:
o Ascalaph Designer
o CST STUDIO SUITE (TM)
o CoNTub
o Deneb
o Ninithi
o NEMO 5 (Nano-ElectronicModeling)

9. NEMO 5 Simulation Tool
NEMO 5 is a simulation tool available in the
Quantum Dot Lab of nanoHub organization.
organization established by a co-operation of
American universities for the purpose of
providing computational and
other educational tools for free for
researchers & students interested in
nanoscience & nanotechnology.

10. The process of simulation is done
by sending the input parameters
of the structure online, then the
supercomputers that exist on the
organization’s site will verify the
data processing and send the
results online to be showed.

11. Definition of the Problem
A simple typical GaAs structure for a cubic
quantum dot is chosen to compute its
energy states & wavefunctions
- The length of the dot in x-direction =11nm; in the
y-direction = 11.5nm and in the z-direction = 5nm.
- The lattice constant = 0.565nm.
- Typical effective mass = 0.067.

12. Computations & Results
The previous parameters of the GaAs are
enrolled in the interface of NEMO 5 and the
:process yielded the following results
:1.The Energy States & Band Structure

13. 2. The Electron Wavefunctions :
Ground state wavefunction 1st excited wavefunction 2nd excited wavefunction
3rd excited wavefunction

14. Conclusions
1. Nanoscience is a rapidly developing field which is the
mainstream for emerging future nanotechnologies with important
applications in different fields of vital importance that can have
strong impact on human life.
2. Due to the difficulties and precisions required in fabricating
nano-structures that can have useful applications, computer
simulations acquire a very important rule that should precede any
fabrication process to reduce costs and enhance success in
producing the required nanodevice designs within a reasonable
time scale.
3. There are many computer simulation tools available at present.
All of these tools rely on quantum mechanical models and
solution methods for the many-body problem embodied in
simulating the behavior of a nano-structure. The present work
shows that the computational tools available freely on the
nanoHub consortium of American universities can be used
successfully to perform such simulations. This is emphasized by
the application of the program NEMO 5 to simulate the behavior
of a particular quantum dot nano-structure constructed from
GaAs semiconductor material.

15. Future Work
1. Extending the use of the NEMO 5 program for a much wide range of
quantum dots, like multi-layered quantum dots.
2. Exploring the possibility of learning how to use other useful programs,
tools and other literature that exist in the NanoHub website with the purpose
of performing more needed simulations for actual nanodevices.
3. Performing a more realistic computer simulation process for the GaAs
quantum dot studied in the present work in such a way that some of the
various input parameters are varied and their effect on the band gap, band
structure, etc. is observed. This could help to illustrate how NEMO 5 can play
a role in any optimization of physical properties of quantum dots towards
actual device fabrication in the future.
4. There are a few other computer programs which can possibly being used
for purposes of extending the computer modeling and simulation work for
quantum dots and other nano-structures. We point particularly in this respect
to Virtual Nano-Lab and the Atomistix Tool Kit computer package developed
and marketed by Quantumwise company, and the importance and usefulness
of its possible future use.