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Conduction Mechanism in Semiconductors
What happens when electrons in the valence band of a semiconductor gain energy?
They can jump the forbidden gap and enter the conduction band.
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Band Structure of Semiconductors
How do metals differ in band structure compared to semiconductors?
Metals have overlapping bands and no forbidden zone.
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Doping Process in Semiconductors
What happens when a pure semiconductor is doped with a pentavalent impurity?
Four out of five valence electrons bond with the semiconductor, and the fifth electron is set free, donating a free electron for conduction.
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Conduction Mechanism in Semiconductors
What occurs when the temperature rises in a semiconductor?
Few electrons become unbounded and free to move, creating holes in the lattice.
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Charge Carriers: Electrons and Holes
What are the charge carriers in a semiconductor?
Free electrons and holes, which are equal in number.
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Intrinsic Semiconductors
What is the behavior of an intrinsic semiconductor at 0 Kelvin?
It behaves like an insulator.
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Types of Semiconductors
What characterizes an N-Type Semiconductor?
Mainly due to electrons, with majority carriers being electrons and minority carriers being holes.
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Band Structure of Semiconductors
What determines the electron energy levels in a solid?
The quantum numbers of the electrons.
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Fermi Level in Semiconductors
What is the Fermi level in semiconductors?
The highest occupied molecular orbital at absolute zero, located between the valence and conduction bands.
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Band Structure of Semiconductors
What determines the number of levels within an energy band?
The number of atoms present.
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Charge Carriers: Electrons and Holes
What are the majority and minority carriers in a P-Type Semiconductor?
Majority carriers are holes and minority carriers are electrons.
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Doping Process in Semiconductors
What is the typical ratio of dopant atoms to pure semiconductor atoms?
Usually, 1 atom in 10^7 is replaced by a dopant atom.
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Band Structure of Semiconductors
What is the significance of the energy gap (E_g) in classifying materials?
If E_g is less than 3.5 eV, the material is classified as a semiconductor; if larger, it is an insulator.
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Types of Semiconductors
What are some examples of semiconductors?
Gallium arsenide, germanium, and silicon.
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Band Structure of Semiconductors
Do similar remarks about bonding and antibonding states apply to other semiconductors?
Yes, similar remarks apply to the bands in Ge, C, and other semiconductors.
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Doping Process in Semiconductors
What is the role of doping in semiconductors?
To modify their electrical properties for devices like switches and amplifiers.
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Properties of Semiconductors
How does the density of electrons compare to the density of holes in intrinsic and extrinsic semiconductors?
In intrinsic semiconductors, the density of electrons equals the density of holes; in extrinsic semiconductors, they do not.
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Conduction Mechanism in Semiconductors
What occurs when electrons are excited across the energy gap?
Electrons populate the conduction band, and holes are created in the valence band, allowing current to flow.
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Band Structure of Semiconductors
What do the valence and conduction bands in semiconductors correspond to?
They correspond to the bonding and antibonding bands of the corresponding atomic valence states.
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Band Structure of Semiconductors
What hybrid states result in the valence and conduction bands in silicon?
The bonding and antibonding states of the hybrid 3s and 3p orbitals.
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Intrinsic Semiconductors
What happens to covalent bonds at absolute zero temperature?
Covalent bonds are very strong, and there are no free electrons, making the semiconductor behave as a perfect insulator.
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Intrinsic Semiconductors
What are the most common intrinsic semiconductor elements?
Germanium (Ge) and Silicon (Si).
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Charge Carriers: Electrons and Holes
How do holes and electrons compare in terms of magnitude?
They are equal in magnitude but opposite in polarity.
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Properties of Semiconductors
What is the difference in electrical conductivity between intrinsic and extrinsic semiconductors?
Intrinsic semiconductors have low conductivity, while extrinsic semiconductors have high conductivity.
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Properties of Semiconductors
What factors influence the conductivity of extrinsic semiconductors?
Conductivity depends on temperature as well as the amount of impurity.
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Definition of Semiconductors
What are semiconductors?
Materials with conductivity and resistivity between conductors and insulators.
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Charge Carriers: Electrons and Holes
What causes charge carriers in semiconductors?
External energy, such as thermal agitation.
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Properties of Semiconductors
How does temperature affect the conductivity of semiconductors?
Resistance decreases with increasing temperature.
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Intrinsic Semiconductors
What are intrinsic semiconductors made of?
Very pure materials made of a single type of element.
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Band Structure of Semiconductors
What is the concept of energy bands in solids?
Electrons in an atom split into multiple energy levels when forming a lattice.
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Band Structure of Semiconductors
What does the forbidden gap represent?
A range of energies that possess no electron.
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Intrinsic Semiconductors
What happens to an intrinsic semiconductor at temperatures greater than 0 Kelvin?
Four thermally generated electron pairs are created.
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Conduction Mechanism in Semiconductors
What is the effect of thermal energy on a semiconductor's conductivity?
It can ionize a few atoms in the lattice, resulting in less conductivity.
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Band Structure of Semiconductors
What are the two important bands in semiconductor terminology?
The valence band and conduction band.
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Band Structure of Semiconductors
What happens to the energy states when two hydrogen atoms form a molecule?
The atomic 1s state splits into a low-energy bonding state and a high-energy antibonding state.
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Band Structure of Semiconductors
What happens to electron energy levels in a conglomeration of atoms of the same type?
They separate into bands of energy levels.
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Doping Process in Semiconductors
What occurs when a pure semiconductor is doped with a trivalent impurity?
Three valence electrons bond with three of the semiconductor's electrons, leaving an absence of an electron (hole).
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Conduction Mechanism in Semiconductors
How does the conductivity of semiconductors compare to metals?
The conductivity of semiconductors is small compared to metals due to the limited number of electrons and holes.
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Band Structure of Semiconductors
How does temperature affect the energy gap of a semiconductor?
The energy gap varies slightly with temperature due to changes in lattice constants from thermal expansion.
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Properties of Semiconductors
What unique property do semiconductors have?
They can conduct electricity under preferable conditions.
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Charge Carriers: Electrons and Holes
What are the majority and minority carriers in an N-Type Semiconductor?
Majority carriers are electrons and minority carriers are holes.
p.3
Types of Semiconductors
What characterizes a P-Type Semiconductor?
Mainly due to holes, with majority carriers being holes and minority carriers being electrons.
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Charge Carriers: Electrons and Holes
What happens to charge carriers when the temperature rises above absolute zero?
They begin to occupy states above the Fermi level.
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Band Structure of Semiconductors
What are the primary band-structure parameters of a semiconductor?
The effective masses of electrons and holes (m_e and m_h) and the energy gap (E_c).
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Band Structure of Semiconductors
How many electrons are required to fill the first band?
2N electrons, where N is the number of atoms.
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Band Structure of Semiconductors
What defines a semiconductor in terms of its energy bands at 0K?
The valence band is completely full, and the gap above it is small, allowing thermal excitation of electrons to the conduction band.
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Types of Semiconductors
How is an extrinsic semiconductor classified?
Into N-type and P-type semiconductors.
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Intrinsic Semiconductors
What happens to valence electrons above absolute zero temperature?
Some valence electrons jump into the conduction band, making the semiconductor behave like a poor conductor.
