HETEROGENEOUS AND HOMOGENEOUS GROWTH

• Homepitaxy  - growth of the same material as the substrate, example: Si on Si
• Heteroepitaxy  - the grown film is different from the substrate
  • Commensurate growth (matched lattice) - small differences between the two lattices (small f = lattice misfit)
  • Incommensurate growth (relaxed lattice) - high f - defects appear
  • Pseudomorphic growth (strained lattice) - high f - less defects, but high stress exists
    • Layer strains to match the substrate
    • in order for the lattice to strain, it is necessary that the adatom/adatom interaction to be low in comparison to the adatom/surface interaction

, where a₀(s ) characterises the substrate lattice and a₀(f ) characterises the film lattice

Example:

Example: SiGe on Si

• SiGe film is strained at the interface and then at higher thickness it becomes relaxed (with defects)
• when the accumulated misfit f*thickness = a₀/2, then the film is relaxed and dislocations (defects) appear
• A critical thickness can be defined as the thickness where the film becomes relaxed
• the critical thickness depends on impurities and composition (for example decreases with increasing germanium content in SiGe)