1. QUANTUMDOTS
Presented by:
Ashok Kumar Jangid
Mphil./PhD. Nanosciences
Centre for Nanosciences
(ashok4483@gmail.com)

2. Introduction & Brief history
Quantum detection & Its optical properties
How they are made ???
Applications
Outlines

3. What are the ???
Quantum dots are semiconductor Nano crystals
They are made of many of the same materials as ordinary semiconductors
They are small and nearly zero dimensional

4. History of Q Dots
• Research into semiconductor colloids began in the early 1960s.
• Quantum dot research has been steadily increasing since then, as evidenced by the
growing number of peer-reviewed papers.
• In the late ‘90s, companies began selling quantum dot based products, such as
Quantum Dot Corporation.
• 2004 - A research group at the Los Alamos Laboratory found that QDs produce 3 electrons per
high energy photon (from sunlight).

5. Quantum confinement
 In semiconductors those diameter is smaller than size of exciting bohr radius, the
excitation are compress, leading to quantum detection (confinement)
 The energy levels can then be modeled using the particle in a box model in which
the energy of different states is dependent on the length of the box. Quantum dots
are said to be in the 'weak confinement regime' if their radii are on the order of the
exciton Bohr radius; quantum dots are said to be in the 'strong confinement regime' if
their radii are smaller than the exciton Bohr radius. If the size of the quantum dot is
small enough that the quantum confinement effects dominate (typically less than
10 nm), the electronic and optical properties are highly tunable.
 The emission and absorption spectra corresponding to the energy band gap of the
quantum dot is governed by quantum confinement principles in an infinite square
well potential.
 The energy band gap increases with a decrease in size of the quantum dot.

6. Bands and Band gap

7. Optical properties
 The Nano crystal's quantum confined size is more significant at energies near the band
gap. Thus quantum dots of the same material such as CdTe, but with different sizes, can
emit light of different color. The physical reason is the quantum confinement effect.
 The coloration of quantum dots are directly related to energy levels. the band gap energy
that determines the energy (and hence color) of the fluorescent light is inversely
proportional to the size of the quantum dot. Larger quantum dots have more energy levels
which are also more closely spaced.

8. How they are made ???
Colloidal synthesis
Electron beam lithography
Molecular beam apitaxy

9. How they are made ???
 Colloidal Synthesis: This method can be used to create large numbers of
quantum dots all at once. Additionally, it is the cheapest method and is
able to occur at non-extreme conditions.
 Electron-Beam Lithography: A pattern is etched by an electron beam
device and the semiconducting material is deposited onto it.
 Molecular Beam Epitaxy: A thin layer of crystals can be produced by
heating the constituent elements separately until they begin to evaporate;
then allowing them to collect and react on the surface of a wafer.

10. Computing
Biology
Photovoltaic devices
Light emitting devices
Applications

11. Conclusion
 QUANTUM DOTS exhibit quantum mechanical properties.
 There are several ways to confine excitons in semiconductors, resulting in
different methods to produce quantum dots.
 Research effort around the world is being applied to expanding the
accuracy and capabilities of this Nano Particles for its usage in the
industry of Hardware Components and Electronics as it is one of the most
promising candidates for use in solid-state quantum computation.
 Quantum dots have also been suggested as implementations of qubits
for Quantum Information Processing.