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Advanced Semiconductor Physics EE 698D Fall 2004 SUMMARY Debdeep Jena, EE 698D Topics Covered • Semiconductor Bandstructure & Effective Mass Approximation • Phonons/Lattice Vibrations • Electronic Transport • Optical Properties • Quantum Confined Structures & Device Applications Debdeep Jena, EE 698D Semiconductor Bandstructure Silicon GaAs GaN Debdeep Jena, EE 698D Bandstructure – k.p • Most of the action happens very close to the CB & VB edges • k.p theory ideal to handle such cases From Notes Debdeep Jena, EE 698D Bandstructure – more accurate methods • Empirical Pseudopotential Method • LCAO methods Silicon GaAs Debdeep Jena, EE 698D Phonons / Lattice Vibrations Phonon Dispersion of a typical semiconductor velocity wavevector (Dipsersion) Acoustic Phonons: v s k (Sound velocity) Optical Phonons: 0 (Dispersionless) Debdeep Jena, EE 698D Transport – Depends on Bandstructure, Phonons, Defects Example : GaN Debdeep Jena, EE 698D Transport – Scattering and Velocity – field curves • Low-field: Mobility • High field – Velocity Saturation, Optical Phonon emission Debdeep Jena, EE 698D Table of Scattering Processes Debdeep Jena, EE 698D Theoretical Formalism Debdeep Jena, EE 698D Theoretical Formalism – Contd… Debdeep Jena, EE 698D Theoretical Formalism – Contd… Debdeep Jena, EE 698D Theoretical Formalism – Contd… FERMI’S GOLDEN RULE Debdeep Jena, EE 698D Transport in a Silicon MOSFET Electron Distribution in k-space Electron Distribution in Real-Space Debdeep Jena, EE 698D Ballistic Transport – Electrons as waves Electrons flow and “diffract” like Waves on surface of water… Debdeep Jena, EE 698D Optical Properties Photons Transverse EM Wave Defined by vector potential A p2 e Electron-photon interaction H (A p) 2m* m Fermi's Golden Rule Absorption Coefficient direct ~DOS(E ) Debdeep Jena, EE 698D Light in periodic structures… Photonic Bandgap Crystals Debdeep Jena, EE 698D Bandgaps for light… Debdeep Jena, EE 698D Quantum Confined Structures Debdeep Jena, EE 698D Quantum Confined Structures Epitaxial 0-D (Quantum Dots) Nanowire Superlattices Nanotubes – 1D (Quantum Wires) Nanowire “Combs” Debdeep Jena, EE 698D Bulk Semiconductor – Device Applications Today’s HBT The First Transistor (1947) Today’s MOSFET Debdeep Jena, EE 698D Quantum – Well Devices GaN HEMTs High-electron Mobility Transistors (HEMTs) GaAs Laser Diodes Debdeep Jena, EE 698D Quantum Well Devices – GaN Solid State Lighting Blu-Ray DVD (GaN QW Laser) White LEDs The New Bulbs! Debdeep Jena, EE 698D Superlattices – Device Applications Quantum Cascade Lasers Debdeep Jena, EE 698D Quantum Well Devices : Organic Semiconductors Flexible Displays (Based on optical transitions in organic QW- structures) Debdeep Jena, EE 698D Quantum Wire Device Applications Nanowire Laser Arrays Nanotube FETs Debdeep Jena, EE 698D Quantum Dot Applications Nanocrystal (Quantum-Dot) Luminescence Spectra Quantum confinement changes emission wavelengths! Debdeep Jena, EE 698D Quantum Dot Applications Today’s Nanocrystals Bio-Applications Stained Glass – Uses quantum-dot dispersion In Glass (19th-century)! Debdeep Jena, EE 698D And Finally… The NEW Christmas Lights! Hope you take away from this class the Excitement of this field … Debdeep Jena, EE 698D
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