Questions and Answers
What is the term applied to any electron that has separated from the fixed lattice structure and has moved to the conduction band?
What is the term used to describe a semiconductor material that has been carefully refined to reduce the number of impurities to a very low level?
What is the main reason for the difference in the number of intrinsic carriers per cubic centimeter for Ge, Si, and GaAs?
What is the main effect of the higher relative mobility of free carriers in GaAs?
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What is the relative mobility of free carriers in GaAs compared to Si?
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What is the number of intrinsic carriers per cubic centimeter in Si at room temperature?
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What is the external cause that can break the covalent bond and free the valence electrons?
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What is the term used to describe the free electrons in a material due only to external causes?
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What is the process of adding impurities to the intrinsic semiconductor material called?
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What is the type of material created by introducing impurity elements having five valence electrons?
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What is the term used to describe the impurities with five valence electrons in n-type material?
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What is the process by which a valence electron acquires sufficient kinetic energy to break its covalent bond and fills the void created by a hole?
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In an n-type material, what is the majority carrier?
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What is the term used to describe the impurities with three valence electrons in p-type material?
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What is the mobility of GaAs in cm²/V-s?
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In a p-type material, what is the majority carrier?
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Study Notes
Covalent Bonds and Free Electrons
- Covalent bonds can be broken when valence electrons absorb sufficient kinetic energy from external natural causes.
- Free electrons are electrons that have separated from the fixed lattice structure and moved to the conduction band.
- Free electrons are sensitive to applied electric fields and potential differences.
Intrinsic Semiconductors
- Intrinsic semiconductors are materials refined to reduce impurities to a very low level.
- Intrinsic carriers are free electrons in a material due only to external causes.
- Intrinsic carriers per cubic centimeter:
- Ge: 2.5×10¹³
- Si: 1.5×10¹⁰
- GaAs: 1.7×10⁶
Relative Mobility of Free Carriers
- The relative mobility of free carriers in a material is their ability to move throughout the material.
- Free carriers in GaAs have more than five times the mobility of those in Si.
- This results in response times of GaAs electronic devices being up to five times faster than those of Si devices.
Extrinsic Semiconductors
- Extrinsic semiconductors are materials subjected to the doping process.
- Doping involves adding impurities to intrinsic semiconductor materials.
- Doping can significantly alter the characteristics of a semiconductor material.
n-type and p-type Materials
- n-type materials are created by introducing impurity elements with five valence electrons (e.g., Antimony, Arsenic, Phosphorus).
- Donor atoms introduce an additional fifth valence electron, which is easily freed for conduction.
- p-type materials are created by introducing impurity elements with three valence electrons (e.g., Boron, Gallium, Indium).
- Acceptor atoms create an incomplete bond pair, resulting in a vacancy for an electron (hole).
Electron-Hole Transfer
- When a valence electron acquires sufficient kinetic energy to break its covalent bond, a hole is created in the covalent bond.
- The hole can then be filled by another electron, resulting in a transfer of holes to the left and electrons to the right.
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Description
Learn about the behavior of valence electrons in covalent bonds, how they can be freed from the lattice structure, and their sensitivity to electric fields.
