Semiconductor doping—donor impurities: From the list {Gold, Phosphorus, Boron, Antimony, Arsenic, Indium}, identify the donor impurities for Si/Ge at room temperature.
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A1, 2, 3
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B1, 2, 4, 6
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C3, 4, 5, 6
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D2, 4, 5
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E1, 3, 6
Answer
Correct Answer: 2, 4, 5
Explanation
Introduction / Context:Donor impurities in group-IV semiconductors (Si, Ge) are typically group-V elements that contribute extra electrons to the lattice, creating n-type material. Distinguishing donors from acceptors and deep-level impurities is key for device design and process control.
Given Data / Assumptions:
- Candidates: Gold (Au), Phosphorus (P), Boron (B), Antimony (Sb), Arsenic (As), Indium (In).
- Host: Si or Ge at room temperature.
Concept / Approach:
Group-V dopants (P, As, Sb) have five valence electrons; substituting into the group-IV lattice leaves one extra electron weakly bound, acting as a donor (n-type). Group-III elements (B, In) are acceptors (p-type). Gold is not a shallow donor in Si/Ge; it introduces deep recombination levels and is often used to control lifetime, not conductivity type.
Step-by-Step Solution:
Identify group of each: P(V), As(V), Sb(V) → donors; B(III), In(III) → acceptors; Au → deep level.Map to indices: 2 (P), 4 (Sb), 5 (As) → donors.Select option listing 2, 4, 5.Verification / Alternative check:
Standard dopant tables list P, As, Sb as n-type dopants in Si/Ge; B, Al, Ga, In as p-type; Au introduces deep traps.
Why Other Options Are Wrong:
- Options including 1 (Au) or 3 (B) or 6 (In) misclassify acceptors/deep levels as donors.
Common Pitfalls:
- Assuming all metals (like Au) donate electrons—deep levels are not shallow donors.
Final Answer:
2, 4, 5