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GATE 2017 EC – Question 19

Electronic Devices · Energy Bands and Carrier Concentration · 1 mark · Multiple choice

A bar of Gallium Arsenide (GaAs) is doped with Silicon such that the Silicon atoms occupy Gallium and Arsenic sites in the GaAs crystal. Which one of the following statements is true?

  1. Silicon atoms act as p-type dopants in Arsenic sites and n-type dopants in Gallium sites
  2. Silicon atoms act as n-type dopants in Arsenic sites and p-type dopants in Gallium sites
  3. Silicon atoms act as p-type dopants in Arsenic as well as Gallium sites
  4. Silicon atoms act as n-type dopants in Arsenic as well as Gallium sites

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Show answer and explanation

Correct answer: (A) Silicon atoms act as p-type dopants in Arsenic sites and n-type dopants in Gallium sites

Explanation

Silicon has 4 valence electrons. On a gallium site (3 valence electrons) it supplies an extra electron, so it is a donor and gives n-type material. On an arsenic site (5 valence electrons) it is one electron short, so it is an acceptor and gives p-type material.