GATE EC 2017 Set 1 — Question 9
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Electronic Devices → Semiconductor Physics → Intrinsic & Extrinsic Semiconductors
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Question
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?
Correct answer
(A) Silicon atoms act as p -type dopants in Arsenic sites and n -type dopants in Gallium sites
Solution
Silicon (Si) is a group IV element. GaAs is a III-V compound semiconductor, where Gallium (Ga) is from group III and Arsenic (As) is from group V.
- When a Si atom (4 valence electrons) replaces a Ga atom (3 valence electrons), it has one extra electron to donate to the conduction band, thus acting as an -type dopant.
- When a Si atom (4 valence electrons) replaces an As atom (5 valence electrons), it has one fewer electron than required for the bonds, thus creating a hole and acting as a -type dopant.
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