1. Quantum Dot Lasers
ASWIN S
ECE S3
Roll no 23

2. .Quantum Dot Lasers (QDL)
CONTENTS
.Quantum Dots (QD)
Confinement Effect
Fabrication Techniques
.Quantum Dot Lasers (QDL)
Historical Evolution
Predicted Advantages
Basic Characteristics
Application Requirements
Conclusion

3. Quantum Dots (QD) Semiconductor nanostructures
Size: ~2-10 nm or ~10-50 atoms
in diameter
Motion of electrons + holes = excitons
Confinement of motion can be created by:
Electrostatic potential
e.g. in e.g. doping, strain, impurities,
external electrodes
the presence of an interface between different
semiconductor materials
e.g. in the case of self-assembled QDs
the presence of the semiconductor surface
e.g. in the case of a semiconductor nanocrystal
or by a combination of these

4. QD – Fabrication Techniques
Core shell quantum structures
Self-assembled QDs and Stranski-Krastanov growth
MBE (molecular beam epitaxy)
MOVPE (metalorganics vapor phase epitaxy)
Monolayer fluctuations
Gases in remotely doped heterostructures

5. QD Lasers – Historical Evolution

6. QDL – Predicted Advantages
Wavelength of light determined by the energy levels not by bandgap energy:
improved performance & increased flexibility to adjust the wavelength
Maximum material gain and differential gain
Small volume:
low power high frequency operation
large modulation bandwidth
small dynamic chirp
small linewidth enhancement factor
low threshold current
Superior temperature stability of I threshold
I threshold (T) = I threshold (T ref).exp ((T-(T ref))/ (T 0))
High T 0  decoupling electron-phonon interaction by increasing the intersubband separation.
Undiminished room-temperature performance without external thermal stabilization
Suppressed diffusion of non-equilibrium carriers  Reduced leakage

7. QDL – Basic characteristics
Components of a laser
An energy pump source
electric power supply
An active medium to create population inversion by pumping mechanism:
photons at some site stimulate emission at other sites while traveling
Two reflectors:
to reflect the light in phase
multipass amplification

8. QDL – Application Requirements
Same energy level
Size, shape and alloy composition of QDs close to identical
Inhomogeneous broadening eliminated  real concentration of energy states obtained
High density of interacting QDs
Macroscopic physical parameter  light output
Reduction of non-radiative centers
Nanostructures made by high-energy beam patterning cannot be used since damage is incurred
Electrical control
Electric field applied can change physical properties of QDs
Carriers can be injected to create light emission

9. CONCLUSION
During the previous decade, there was an intensive interest on the development of quantum dot lasers. The unique properties of quantum dots allow QD lasers obtain several excellent properties and performances compared to traditional lasers and even QW lasers.
Although bottlenecks block the way of realizing quantum dot lasers to commercial markets, breakthroughs in the aspects of material and other properties will still keep the research area active in a few years. According to the market demand and higher requirements of applications, future research directions are figured out and needed to be realized soon.