Kursthemen

  • Introduction

    Alles einklappen Alles aufklappen

    Epitaxy, i.e. the ordered growth of one material on top of a crystalline substrate, is a key process in semiconductor technology, ubiquitously used for the fabrication of high-quality films and hetero-structures of complex design. This course provides a general introduction to the physics of epitaxial growth, offering an overview of the key thermodynamic and kinetic factors driving the formation of thin-films rather than three-dimensional micro- or nano-structures during material deposition. Such theoretical aspects will be presented from an applied perspective, constantly related to the experimental observations with the purpose of providing to students and growers useful guide-lines for the interpretation and tuning of experiments. 
    After a general description of epitaxy, recalling its basic principles, experimental conditions and applications, a few lessons will cope with the thermodynamic aspects describing the crystal morphology and stability for both homoepitaxial and heteroepitaxial systems. Then, the atomistic mechanisms leading to the growth will be reviewed. Finally, the mechanisms of self-assembly of nanostructures will be discussed.

  • 1. Epitaxy: general concepts

    • what is epitaxy?
    • applications and advantages

  • 2. Methods of Epitaxy

    • Thermodynamics of growth: supersaturation and supercooling
    • experimental methods: LPE, VPE, MOVPE, MBE
    • characterization techniques: STM/AFM, LEED, RHEED

  • 3. Surface energy and equilibrium crystal shape

    • surface energy
    • principles of Wulff construction and examples
    • estimate of surface energy by ab-initio and role of chemical potential

  • 4. Crystal on a substrate, wetting / dewetting

    • growth mode and capillarity model
    • Young law for contact angle and conditions of wettability
    • Wetting/Dewetting with examples

  • 5. Continuum models of morphological evolution

    • Mullins model: thermal smoothing
    • Gibbs-Thompson chemical potential and kinetic pathway of faceted shapes and examples
    • Kinetic effects and Kinetic Wulff shape

  • 6. The Asaro-Tiller-Grinfeld instability and beyond

    • derivation of ATG in 2D
    • critical and fastest instability mode (dependence on composition)
    • limitations

  • 7. Nucleation theory

    • surface vs. volume energy and critical nucleus
    • density as a function of diffusion and deposition rates
    • scaling laws
    • mean-field rate equations

  • 8. Islanding and Stranski Krastanov growth

    • strain relaxation by facets and role of aspect-ratio
    • wetting layer vs islands
    • island types and shape transitions

  • 9. Dislocations in Semiconductors

    • types of dislocations
    • effect of free-surfaces on dislocations

  • 10. Plastic relaxation in epitaxy

    • dislocations in films and critical thickness
    • dislocated islands

  • 11. Modeling growth at the atomic scale

    • deposition
    • adatom diffusion
    • Concept of KMC
    • Solid on solid approach and modeling of growth regimes
    • Examples

  • 12. Step dynamics

    • step-flow vs layer-by-layer mode
    • adatom diffusion across steps
    • Burton Cabrera Frank model
    • Ehrlich-Schwoebel barrier
    • step bunchings

  • 13. Self assembly and nanostructures: QD, QW,NW

    • ordering and substrate patterning
    • selective area epitaxy

  • 14. Droplet epitaxy and NW growth

    • droplet epitaxy
    • VLS growth of NWs
    • core-shell structures