Epitaxial growth

Which is closest to the density of threading dislocations, which run up to the film surface, in GaN grown on sapphire?

  1. AAbout 10²⁰ cm⁻²
  2. BAbout 10¹ to 10² cm⁻²
  3. CAbout 10⁸ to 10⁹ cm⁻²
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Answer: C. About 10⁸ to 10⁹ cm⁻²

Sapphire and GaN have very different lattice constants, so GaN on sapphire contains high densities of threading dislocations, about 10⁸ to 10⁹ cm⁻². That InGaN LEDs still emit efficiently is thought to be because composition fluctuations in the InGaN layer localize carriers so they rarely reach dislocations.

  • A. About 10²⁰ cm⁻² approaches atomic density and could not form a crystal.
  • B. About 10¹ to 10² cm⁻² is nearly dislocation-free, very high-quality crystal.
  • C. Correct. A high density of about 10⁸ to 10⁹ cm⁻².
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More Epitaxial growth questions

  1. In bipolar transistors and similar devices, what is the main purpose of a heavily doped layer (buried layer) beneath the epitaxial layer?
  2. Which is closest to the typical growth temperature for SiC epitaxy (CVD)?
  3. Which type of reactor is mainstream for silicon epitaxial growth on 300 mm wafers?
  4. In heteroepitaxy of materials with very different lattice constants, what is the purpose of inserting a "graded buffer layer" whose composition changes gradually?
  5. 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?