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1. Chemistry and Materials Research www.iiste.org
ISSN 2224- 3224 (Print) ISSN 2225- 0956 (Online)
Vol 2, No.1, 2012
Electronic Properties of Nanostructured Quantum Dots
Syed Bahauddin Alam, Md. Didarul Alam, Tahnia Farheen, Md. Abdullah-Al-Mamun, Md.
Rashiduzzaman Bulbul, K M Mohibul Kabir, Farha Sharmin†, Hasan Imtiaz Chowdhury, Md. Abdul Matin
Department of EEE, Bangladesh University of Engineering and Technology (BUET), Dhaka
†Development Research Network (D.Net)
baha_ece@yahoo.com
Abstract
In this paper, property analysis of quantum dot cuboid nanocrystals with different nanostructures are shown
by simulation results for particular device structure and boundary conditions of Light and dark Transitions
for the X, Y and Z- Polarized for different structures and so forth. EOM is a systematic method to derive
analytic expressions for GF Wise (sometimes) extrapolation of perturbation theory. Applied to Anderson
model, excellent for not-too-strong correlations fair qualitative picture of the Kondo regime
self-consistency improves a lot. Finally from the simulation, it is evident that, the characteristics are almost
equivalent for different nanostructures for a particular boundary condition. In this paper electronic
properties of nanostructured quantum dots are analyzed.
Keywords: Quantum dot, nanocrystals, nanostructure.
1. Introduction
A quantum dot is a semiconductor nanostructure that confines the motion of conduction band electrons,
valence band holes, or excitons (pairs of conduction band electrons and valence band holes) in all three
spatial directions. A quantum computer is any device for computation that makes direct use of distinctively
quantum mechanical phenomena, such as superposition and entanglement, to perform operations on data.
The quantum properties of particles can be used to represent and structure data and that quantum
mechanisms can be devised and built to perform operations with these data. Any solid material in the form
of a particle with a diameter is comparable to the wavelength of an electron. Quantum Dots is man-made
artificial atoms that confine electrons to a small space. As such they have atomic-like behavior and enable
the study of quantum mechanical effects on a length scale that is around 100 times larger than the pure
atomic scale. Quantum dots offer application opportunities in optical sensors, lasers, and advanced
electronic devices for memory and logic. Quantum dots were predicted to exhibit interesting cooperative
behavior in many-dot systems with overlapping wave functions, due to the resulting miniband structure,
and also as elements in cellular neural networks .However, no scheme for using discrete quantum dots for
computing was proposed during this period. These “dots” were not quantum dots in the energy quantization
sense, but rather relied on their ultra small capacitance, which was a consequence of their very small size,
to reveal measurable voltage changes with charge variations of only a single electron. Such behavior is
classical, except for tunneling between dots. In confined semiconductor dots, the energy quantization is
superimposed on the Coulombic effects, but is not the primary phenomenon of interest. At the heart of the
fluorescence of Quantum dot nanocrystals is the formation of excitons, or Coulomb correlated electron-hole
pairs. The exciton can be thought of as analogous to the excited state of traditional fluorophores; however,
excitons typically have much longer lifetimes (up to ~µseconds), a property that can be advantageous in
certain types of "time-gated detection" studies. Yet another distinction arises from the direct, predictable
relationship between the physical size of the quantum dot and the energy of the exciton (therefore, the
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2. Chemistry and Materials Research www.iiste.org
ISSN 2224- 3224 (Print) ISSN 2225- 0956 (Online)
Vol 2, No.1, 2012
wavelength of emitted fluorescence). This property has been referred to as "tuneability", and is being
widely exploited in the development of multicolor assays. Quantum dot nanocrystals are also extremely
efficient machines for generating fluorescence; their intrinsic brightness is often many times that observed
for other classes of fluorophores. Another practical benefit of achieving fluorescence without involving
conjugated double-bond systems is that the photostability of Quantum dot nanocrystals is many orders of
magnitude greater than that associated with traditional fluorescent molecules; this property enables
long-term imaging experiments under conditions that would lead to the photo-induced deterioration of other
types of fluorophores. The main objective of our experiment was to Study and understand the electronic
properties of coupled quantum dots and to determine the coupling between these dots using vertical electric
fields. For that, we have to assemble optical techniques of Photocurrent Measurements and
Photoluminescence. Single quantum dot ensembles are: PC technique successfully applied to single layer of
quantum dots, Stark Shifts and Oscillator Strengths. But we have to sort out for coupled quantum dot.
2. Electronic Structure and Dimensions
For Optical Excitation, the characteristics of Exciton are it is bound electron-hole pair and for the Excite
semiconductor, it is creation of electron-hole pair. There are postulates behind these: There is an attractive
potential between electron and hole. In hydrogenic system, mass of hydrogen is greater than electron and
from Bohr Theory, Binding energy is determined. The excitons confined to the dot are discrete energies and
Degree of confinement determined by dot size and Exciton absorption is function-like peaks in absorption.
Now for the clarity of the nanostructure of dot, an analysis on comparison between Bits and Quantum bits
are discussed. These are: a Quantum bit can hold a one, a zero, or, crucially, a superposition of these. A
classical computer has a memory made up of bits, where each bit holds either a one or a zero. The Quantum
bits can be in a superposition of all the classically allowed states. The register is described by the phases of
the numbers can constructively and destructively interferes with one another; this is an important feature for
quantum algorithms. For an n quantum bit quantum register, recording the state of the register requires 2n
complex numbers (the 3-quantum bit register requires 23 = 8 numbers). Consequently, the number of
classical states encoded in a quantum register grows exponentially with the number of Quantum bits. For
n=300, this is roughly 1090, more states than there are atoms in the observable universe. Electronic structure
can be Formed during epitaxial growth of lattice mismatched materials e.g. InAs on GaAs (7% lattice
mismatch) and Form due to kinetic and thermodynamic driving forces – energetically more favourable to
form nanoscale clusters of InAs. Some general properties are: Perfect crystalline structures, High areal
density (10-500µm-2), Strong confinement energies (100meV), Lasers (Jth<6Acm-2) in visible and near
infrared, Quantum Information and Cryptography, For SAQDs - z-axis confinement is generally much
stronger than transverse quantisation x,y (Ez>>Exy). QD states are often approximated as a 2D Harmonic
oscillator potential – Fock-Darwin states. Orbital character of QD states similar to atomic systems. The
shells n=1,2,3 - often termed s,p,d,.. in comparison with atomic systems. Dipole allowed optical transitions
Dn=0. Single X transitions observable in absorption experiment. QDs should be self-assembled (for
economic gains, not quite in reach of nano-lithography) for the reasons of semiconductor with smaller
bandgap embedded into matrix with large bandgap, just right size, large enough to accommodate an exciton,
small enough in all directions for quantum confinement, no structural defects such as dislocations. The key
factor here is uniformities of size, shape, chemical composition, strain distribution, crystallographic phase,
and mutual alignment. For optoelectronics, there is no contacting problem, only problem QD array
homogeneity, active medium in lasers, (In,Ga,Al)As based 1.3 µm, far infrared detectors, novel device
concepts such as quantum cellular automata, Isolation of a single Quantum Dot, Emission spectroscopy,
and Power-dependence reveals the different configurations.
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3. Chemistry and Materials Research www.iiste.org
ISSN 2224- 3224 (Print) ISSN 2225- 0956 (Online)
Vol 2, No.1, 2012
2. Dimensions and Results
For a free electron, 3/2kBT = Ñ2k2/2ml ~ 60, for quantum effects: ~10s; in semiconductors, use me* (effective
mass) instead: me */me ~ 1/10, for quantum effects: 100s Þ (10s nm). The number of atoms ~ 103 - 106 .
Properties are determined by size of Quantum dots. Small quantum dots, such as colloidal semiconductor
nanocrystals, can be as small as 2 to 10 nanometers, corresponding to 10 to 50 atoms in diameter and a total
of 100 to 100,000 atoms within the quantum dot volume. At 10 nanometers in diameter, nearly 3 million
quantum dots could be lined up end to end and fit within the width of a human thumb. Quantum wires,
which confine the motion of electrons or holes in two spatial directions and allow free propagation in the
third. Quantum wells confine the motion of electrons or holes in one direction and allow free propagation in
two directions. Both have a discrete energy spectrum and bind a small number of electrons. In contrast to
atoms, the confinement potential in quantum dots does not necessarily show spherical symmetry. In
addition, the confined electrons do not move in free space but in the semiconductor host crystal play an
important role for all quantum dot properties. In contrast to atoms, the energy spectrum of a quantum dot
can be engineered by controlling the geometrical size, shape, and the strength of the confinement potential.
it is relatively easy to connect quantum dots by tunnel barriers to conducting leads. If now Motion
technique applied to quantum dot models, according to the Anderson model
Here Generalizations are structured leads (“mesoscopic network”), multilevel dots / multiple dots with
capacitative / tunneling interactions, Spin-orbit interactions and many-body interactions restricted to the dot
are essential. We have to treat Anderson model using Perturbation theory (PT) in Γ, tricky to extend into
strong coupling (Kondo) regime, Map to a spin model and do scaling, Numerical Renormalization Group
(NRG), accurate low energy physics, integrability condition too restrictive, finite T laborious, Equations of
motion (EOM).
3. Conclusion
The main objective of our experiment was to study and understand the electronic properties of coupled
quantum dots and to determine the coupling between these dots using vertical electric fields. In this paper
electronic properties of nanostructured quantum dots are analyzed. Finally from the simulation, it is evident
that, the characteristics are almost equivalent for different nanostructures for a particular boundary
condition. In this paper electronic properties of nanostructured quantum dots are analyzed.
References
Syed Bahauddin Alam et. al, Modeling of Physics of Beta-Decay using Decay Energetics, in American
Institute of Physics (AIP) Proceedings, 2012.
Syed Bahauddin Alam et. al Dosimetry Control and Electromagnetic Shielding Analysis, in American
Institute of Physics (AIP) Proceedings, 2012.
Syed Bahauddin Alam et. al Transient and Condition Analysis for Gen-4 Nukes for Developing Countries,
in American Institute of Physics (AIP) Proceedings, 2012.
Syed Bahauddin Alam et al., Methodological Analysis of Bremmstrahlung Emission , published in the
World Journal of Engineering and Pure and Applied Science, pp: 5-8,Volume: 1, Issue: 1 , Research |
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4. Chemistry and Materials Research www.iiste.org
ISSN 2224- 3224 (Print) ISSN 2225- 0956 (Online)
Vol 2, No.1, 2012
Reviews | Publications, June 2011.
Syed Bahauddin Alam et al., Mathematical Analysis of Poisoning Effect, published in the World Journal of
Engineering and Pure and Applied Science, pp: 15-18, Volume:1, Issue: 1 Research | Reviews |
Publications , June 2011.
Syed Bahauddin Alam , Md. Nazmus Sakib, Md. Rishad Ahmed, Hussain Mohammed Dipu Kabir, Khaled
Redwan, Md. Abdul Matin, Characteristic and Transient Analysis of Gen-4 Nuclear Power via Reactor
Kinetics and Accelerator Model in 2010 IEEE International Power and Energy Conference, PECON 2010,
pp. 113-118, Malaysia, 29 Nov, 2010.
Syed Bahauddin Alam, Hussain Mohammed Dipu Kabir, Md. Nazmus Sakib, Celia Shahnaz, Shaikh
Anowarul Fattah, EM Shielding, Dosimetry Control and Xe(135)-Sm(149) Poisoning Effect for Nuclear
Waste Treatment in 2010 IEEE International Power and Energy Conference, PECON 2010, pp.
101-106, Malaysia, 29 Nov,2010.
Syed Bahauddin Alam, Hussain Mohammed Dipu Kabir, Md. Rishad Ahmed, A B M Rafi Sazzad, Celia
Shahnaz, Shaikh Anowarul Fattah, Nuclear Waste Transmutation by Decay Energetics, Compton Imaging,
Bremsstrahlung and Nuclei Dynamics in 2010 IEEE International Power and Energy Conference, PECON
2010, pp. 107-112, Malaysia, 29 Nov, 2010.
Syed Bahauddin Alam, Hussain Mohammed Dipu Kabir, A B M Rafi Sazzad, Khaled Redwan, Ishtiaque
Aziz, Imranul Kabir Chowdhury, Md. Abdul Matin, Can Gen-4 Nuclear Power and Reactor Technology be
Safe and Reliable Future Energy for Developing Countries? In 2010 IEEE International Power and Energy
Conference, PECON 2010, pp. 95-100, Malaysia, 29 Nov, 2010.
Syed Bahauddin Alam, Md. Nazmus Sakib, Md Sabbir Ahsan, A B M Rafi Sazzad, Imranul Kabir
Chowdhury, Simulation of Bremsstrahlung Production and Emission Process in 2nd International
Conference on Intelligent Systems, Modelling and Simulation, ISMS2011, Malaysia, Phnom Penh
(Cambodia) , 25-27 Jan, 2011.
Syed Bahauddin Alam, Md. Nazmus Sakib, Md Sabbir Ahsan, Khaled Redwan, Imranul kabir, Simulation
of Beta Transmutation by Decay Energetics in 2nd International Conference on Intelligent Systems,
Modelling and Simulation, ISMS2011, Malaysia, Phnom Penh (Cambodia) , 25-27 Jan, 2011.
Syed Bahauddin Alam, Md. Nazmus Sakib, A B M Rafi Sazzad, Imranul Kabir in Simulation and Analysis
of Advanced Nuclear Reactor and Kinetics Model in 2nd International Conference on Intelligent Systems,
Modelling and Simulation, ISMS2011, Malaysia, Phnom Penh (Cambodia) , 25-27 Jan, 2011.
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