Epitaxial growth

What is the main purpose of epitaxially growing and embedding Si:C (silicon with a small amount of carbon) in the source and drain of nMOS transistors?

  1. ATo reduce gate capacitance
  2. BTo apply compressive strain to the channel and raise hole mobility
  3. CTo use Si:C's smaller lattice constant to apply tensile strain to the channel and raise electron mobility
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Answer: C. To use Si:C's smaller lattice constant to apply tensile strain to the channel and raise electron mobility

Carbon atoms are smaller than silicon atoms, so Si:C has a smaller lattice constant than silicon. Embedding it in the nMOS source and drain pulls on the channel, creating tensile strain that raises electron mobility. For pMOS, SiGe with a larger lattice constant is embedded instead to apply compressive strain.

  • A. It is not meant to reduce gate capacitance.
  • B. Using compressive strain to raise hole mobility is the role of SiGe in pMOS.
  • C. Correct. Tensile strain raises electron mobility.
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More Epitaxial growth questions

  1. Which research-stage technique grows a crystal on a substrate covered with a 2D material such as graphene so that the grown film can be peeled off and the substrate reused?
  2. In epitaxial structures for GaN HEMTs, what is the main purpose of adding carbon or iron to the GaN buffer layer beneath the channel?
  3. When a polar compound semiconductor such as GaAs is grown on a non-polar silicon substrate, what is the boundary called between regions in which the Ga and As positions are inverted?
  4. In SiC epitaxy, what is the phenomenon called in which many atomic surface steps gather into large steps, roughening the surface?
  5. Which correctly describes epitaxial growth?