Semiconductor Materials: Group IV Elements, Carriers & Doping: 25 flashcards
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1. What is a semiconductor?
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A material whose electrical conductivity lies between that of conductors and insulators, typically $10^{-6}$–$10^3$ S/cm.
2. What are the three ways to change semiconductor conductivity?
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Doping, temperature variation, and illumination.
3. Which Group IV elements are the most common elemental semiconductors?
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Silicon (Si), germanium (Ge), and tin (Sn).
4. Why do semiconductors behave as insulators at absolute zero?
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All valence electrons are locked in covalent bonds, so no free carriers exist for conduction.
5. What is a hole in a semiconductor?
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A deficiency of an electron in a covalent bond; it is not a real particle and has no actual positive charge.
6. In a pure semiconductor, what carries the current?
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Both free electrons and holes contribute to conduction.
7. What is the typical band gap range of semiconductors?
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About 0.1 to 3 eV.
8. What is the temperature coefficient of resistivity for semiconductors?
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Negative — resistivity decreases as temperature increases.
9. Do semiconductors obey Ohm's law?
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No, they are nonlinear conductors; their resistance changes with voltage, temperature, and illumination.
10. What is doping?
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The process of adding impurity atoms to an intrinsic semiconductor to increase its conductivity.
11. What is an extrinsic semiconductor?
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A doped semiconductor in which electron and hole concentrations are unequal.
12. Which dopants create n-type semiconductors?
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Pentavalent atoms such as As, P, Sb, and Bi — they act as donors.
13. Which dopants create p-type semiconductors?
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Trivalent atoms such as In, B, Al, and Ga — they act as acceptors.
14. In n-type material, what are the majority and minority carriers?
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Majority carriers are electrons; minority carriers are holes.
15. In p-type material, what are the majority and minority carriers?
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Majority carriers are holes; minority carriers are electrons.
16. Where does the donor level $E_d$ lie in an n-type semiconductor?
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Just below the conduction band $E_c$; the Fermi level lies between them.
17. Where does the acceptor level $E_a$ lie in a p-type semiconductor?
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Just above the valence band $E_v$; the Fermi level lies between them.
18. What is the typical dopant concentration in a doped semiconductor?
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About one dopant atom per $10^7$ host atoms.
19. What are III-V compound semiconductors?
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Binary semiconductors formed when a Group III element combines with a Group V element.
20. What are II-VI compound semiconductors?
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Binary semiconductors formed when a Group II element combines with a Group VI element.
21. Why does diamond remain an insulator at room temperature?
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Its band gap is about 6 eV, too large for thermal energy to lift electrons into the conduction band.
22. What crystal structures do most semiconductors adopt?
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Zinc blende or wurtzite structures with covalent bonding.
23. What happens to covalent bonds at room temperature?
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Thermal oscillations break some bonds, freeing electrons and creating holes.
24. Why is intrinsic semiconductor conductivity too low for devices?
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It has few free carriers, so practical devices need higher, controllable conductivity via doping.
25. What real-world devices rely on semiconductor tunability?
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Diodes, transistors, solar cells, and photodetectors.
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