Epitaxial growth

In heteroepitaxy of materials with very different lattice constants, what is the purpose of inserting a "graded buffer layer" whose composition changes gradually?

  1. ATo make the wafer thinner
  2. BTo change the lattice constant gradually, relaxing strain step by step and reducing dislocations threading into the upper layer
  3. CTo increase the growth rate
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Answer: B. To change the lattice constant gradually, relaxing strain step by step and reducing dislocations threading into the upper layer

Growing a material with a large lattice mismatch directly causes many dislocations to thread up into the top layer. Inserting a buffer with gradually changing composition relaxes the strain step by step, keeping misfit dislocations within the buffer and reducing dislocations in the upper layer. It is used in growing SiGe, III-Vs and others.

  • A. It is not intended to thin the wafer.
  • B. Correct. Strain is relaxed gradually to reduce dislocations in the upper layer.
  • C. It is not intended to increase the growth rate.
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More Epitaxial growth questions

  1. In the X-ray diffraction rocking curve used to evaluate the crystal quality of an epitaxial layer, what does a narrow peak width (FWHM) indicate?
  2. In MOCVD growth of GaN, what does the controlled condition "V/III ratio" mean?
  3. When a lightly doped epi layer is grown at high temperature on a heavily doped substrate, what is the phenomenon called in which substrate dopants seep into the epi layer by solid-state diffusion, smoothing the concentration change at the interface?
  4. Which technique, developed by Isamu Akasaki, Hiroshi Amano and colleagues to grow high-quality GaN on sapphire, first deposits a thin layer at low temperature and then grows GaN at high temperature?
  5. In a lattice-mismatched system, which growth mode grows layer by layer for the first few atomic layers and switches to island growth as strain accumulates? It is also used to make quantum dots.