1. InAs on GaAs self assembled Quantum Dots By KH. Zakeri sharif University of technology, Spring 2003

2. Outline I. introduction II. Method of fabrication III. Physical properties IV. characterization V. Modeling & Simulation VI. Application

3. I. Introduction At first time Reed & coworkers in Texas

4. Method of formation I. Etching & lithography II. Selective growth III. Self assembled ~ self organized

5. Growth System – Molecular Beam Epitaxy (MBE) – Metal-Organic Chemical Vapor Deposition (MOCVD) – Chemical Beam Epitaxy (CBE) Influence of deposition conditions – Deposition mode and misorientation – Growth rate – Group V pressure – High index substrate – Capping layer – Stacking of QDs QD size and density Luminescence Stability Gain saturation QD size and density Luminescence Stability Gain saturation III. Self assembled

6. Quantum Dot Growth Growth modes depends on 1.Interface energy 2.Lattice mismatch FdvM VWSK

7. Placing monolayers of different lattice constants on top of each other can result in a deformation of the deposited layers Essentially a way of relieving stress on the material Under a certain set of parameters, you can create certain deformations called Quantum Dots ~20-30 nm Quantum Dot Growth

8. Physical properties I. Density of state II. Optical absorption & quantum transition III. Energy state

9. e source drain gate N= 2 1 0 N= 2 1 v on off R1 R2 C1 C2 IV. Coulomb Blockade Effect & coulomb oscillation Quantum tunneling of electron between source and drain can be blocked If the charging energy E c = e 2 /2C >> kT c=4   R  E = eV –E c <0: blocked 2E c =e 2 /(C 1 +C 2 )

10. Photoluminescence We can use a laser to excite electrons into the conduction band Recombination will often produce a photon – the energy of this photon tells us what state the electron and hole were in E ECEC EVEV laseremitted light EGEG hν=2.4 eV hν=1.5 eV (GaAs) hν≈1.2 eV (QDs)

11. Experimental Setup Laser – Argon or HeNe diffraction grating Sample dewar 77 Kelvin Spectrometer photo-multiplier tube 77 Kelvin amplifier I E / λ computer diffraction grating

12. InAs Quantum Dots in GaAs [100] GaAs InAs

13. Modeling & simulation Growth simulation 1. Quasi particle 2. Poison – Schrödinger eq. 3. Slater transition Energy Model calculation's Probability density isosurfaces for an electron confined in a QD Kinetic Mont Carlo Molecular Dynamic Random Deposition

14. Structural properties 1.Quantum confined 2.Tight-Bonding 3.Effective mass 4.D.F.T Modeling & simulation Squared pyramid S. Ruvimov et al, PRB 51, 14766 (1995) Truncated pyramid N. Liu et al, PRL 84, 334 (2000) Lens J. Zou et al, PRB 59, 12279 (1999) JM Moisson et al, APL 64, 196 (1994) Ring RJ Warburton et al, Nature 405, 926 (2000) Elongated pyramid W. Yang et al, PRB 61, 2784 (2000) Numerical solution

15. Infra-red detector 1. Military 2. Communication 3. Multistage detector 4. High Optical gain QD laser Diode QD transistors & Devices QD nano oscillatorApplications

16. Thanks for your attention