CLS Abe

1. SRI KRUSHNA CHANDRA GAJAPATI (AUTONOMOUS) COLLEGE
PARALAKHEMUNDI
DEPARTMENT OF PHYSICS
“QUANTUM DOT HETEROSTRUCTURE”
Under the supervision of
NIBEDITA SASMAL
Representator:
1. JOSOBANTA BIDIKA
2. PAPU SAHU
3. BADAL KUMAR PANI
4. DEBASISH PAIK
5. K. KRISHNAMURTHY
PAPER: DSE IV
DATE:

2. OUTLINE
 INTRODUCTION
 FABRICATION OF QDHS
 PROPERTIES OF QDHS
 ADVANTAGES OF QDHS
 APPLICATION
 FUTURE APPROACHES OF QDHS
 CONCLUSION

3. INTRODUCTION
What is a Quantum Dot?
The term quantum dot was coined in 1986.
 A quantum dot is a nanometer-sized
semiconductor particle traditionally with a
core-shell structure.
This Photo by Unknown Author is licensed under CC BY-NC

4. HETEROSTRUCTURE:
Any crystal consisting of one or more junction
between different semiconductors with
different band gaps, lattice constants , and
layer thickness are termed as heterostructure.

5. Quantum Dot Heterostructure(QDHS):
Quantum-dot (QD) heterostructures are
nanoscale coherent insertions of narrow-gap
material in a single-crystalline matrix.
Quantum dot possess atom-like discrete
energy level separated by regions of forbidden
states.
Energy pumped into the system goes to excite
carriers between discrete levels and random
motion.

6. FABRICATION OF QDHS
There are three main way to confine excitons
in semiconductors:
 Lithography
Colloidal synthesis
Epitaxy:
• Patterned growth
• Self-organized growth

7. 1. LITHOGRAPHY
Quantum wells are covered with a polymer
mask and exposed to an electron or ion beam.
The surface is covered with a thin later of
metal, then cleaned and only the exposed
areas keep the metal layer.
Pillars are etched into the entire surface.
Multiple layers are applied this way to build
up the properties and size wanted.

8. 2. COLLOIDAL SYNTHESIS
Emersion of semiconductor microcrystals in
glass dielectric matrices.
Taking a silicate glass with 1% semiconducting
phase(CdS, CuCl, CdSe or CuBr).
Heating for several hour at high temperature.
• Formation of microcrystal of nearly equal size.

9. 3(a). EPITAXY: PATTERNED GROWTH
 Semiconducting
compound with a smaller
band gap (GaAs) are
grown on the surface of a
compound with a larger
band gap(AlGaAs).
 Growth is restricted by
coating it with a masking
compound(SiO2) and
etching that mask with
the shape of the required
crystal cell wall shape.

10. 3(b). EPITAXY: SELF-ORGANIZED
GROWTH
• Uses a large difference in
the lattice constants of
the substrate and the
crystallizing material.
• When the crystallized
later is thicker than the
critical thickness, there is
a strong strength on the
layers.
• The breakdown results in
a randomly distributed
islets of regular shape
and size.

11. PROPERTIES OF QDHS
Within a quantum dot, there are confined
valence band holes, conduction band
electrons, or excitons.
There are particles that carry the electricity
and because of this confinement the quantum
dot has a distinct energy level.
The electrons within a quantum dot have to
occupy an energy level that fits inside it.

12.  When excitation occurs
these elecron emit a
photon.
 Excitation can be
caused by the quantum
dot coming into contact
with a light or
electricity source.
 The longest wavelength
of light produced by
biggest quantum dot
and shortest
wavelength of light are
generated by smallest
quantum dot.

13. ADVANTAGES
• Very narrow spectral lines width, depending
on the quantum dot’s size.
• Multiplexed detection.
• Large absorption coefficient across a wide
spectral range.
• Small size/high surface -to- volume ratio.
• Very high levels of brightness.
• Blinking

14. APPLICATIONS
• Photo voltalic device: Solar Cells
• Biology: Biosensors, imaging
• Light emitting diodes: LEDs
• Quantum computations

15. • Flat-panel displays
• Memory elements
• Photodetectors
• Lasers

16. Future approaches of QDHS:
• Quantum dots are great potential utility in
solar harvesting and light-sensing
technologies.
• Due to their tunable bandgap, they can be
engineered to target a particular range of
wavelengths.

17. CONCLUSION
 Quantum Dot Heterostructure
• Semiconductor particle with a size in the order
of the Bohr’s radius of the excitation.
• Energy level depend on the size of the dot.
 Different method for fabrication quantum dot
• Lithography
• Colloidal synthesis
• Epitaxy

18. References
1. G. Bastard; JA Brum; R Ferreria(1991). “
Figure 10 in Electronic states in
semiconductor heterostructure”. In Henry
Ehrenreich, David Turnbull (ed). Solid state
physics: Semiconductor heterostructure and
Nanostructure. P. 259.