DEFECTS

• Defects at interface - appear only for heteroepitaxy, for homoepitaxy the film is perfect, without defects
  • they propagate in the layer → device failures
  • create states in the energy bandgap and reduce mobility and carrier concentration
  • defect density decreases however with distance from the substrate → as a solution: thick layers can be grown
• Stalking faults - extra or missing plane of atoms (for example ABCABC is the correct order, a stalking fault would be ACABC, in which the plane B is missing - see picture below)

• Cause: they propagate from dislocations or oxides (impurities) from the surface
• Grow in the film as an inverted pyramid (see picture)
• Can be seen on the surface

• Dislocations - are the 2D analog - line defects
  • Caused by lattice misfit, stress at the thickness where incommensurate growth starts
  • Cannot be seen at the surface, can be observed by selective etching which is a distructive method
  • They move by gliding/sliding
  • There are two types, depending on how they move: edge (the whole plane moves in the same time) and screw (the movement starts from a corner)