Quantum Dot Lasers ASWIN S ECE S3 Roll no 23

.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

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

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

QD Lasers – Historical Evolution

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

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

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

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.