The p-type epitaxial layer grown over an n-type substrate for fabricating a bipolar transistor will function as

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  1. The collector of a p-n-p transistor
  2. The base of an n-p-n transistor
  3. The emitter of a p-n-p transistor
  4. The collector contact for a p-n-p transistor

Answer (Detailed Solution Below)

Option 1 : The collector of a p-n-p transistor
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Detailed Solution

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Explanation:

  • Epitaxy refers to the deposition of an overlayer on a crystalline substrate, where the overlayer is in registry with the substrate. The overlayer is called an epitaxial film or epitaxial layer.
  • By growing a lightly doped epi layer over a heavily-doped silicon substrate, a higher breakdown voltage across the collector-substrate junction is achieved while maintaining low collector resistance,
  • It also allows better control of doping concentrations of the devices.

The figure shown below shows the fabrication of a monolithic circuit in which a p-type epitaxial layer is grown onto an n-type substrate which helps in making p-type devices formed by suitable masking and diffusion and the fabricated transistor will have a p-type emitter and collector and n-type base.

F1 Tapesh Anil 20.01.21 D22

Hence, option (1) is correct.

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