Podcast
Questions and Answers
In N-type semiconductors, the majority charge carriers are ______.
In N-type semiconductors, the majority charge carriers are ______.
electrons
P-type semiconductors are created by doping with ______ elements which create holes.
P-type semiconductors are created by doping with ______ elements which create holes.
acceptor
Dopant elements increase the conductivity of semiconductors by providing additional ______.
Dopant elements increase the conductivity of semiconductors by providing additional ______.
charge carriers
As temperature increases, more thermal energy allows for the creation of free ______.
As temperature increases, more thermal energy allows for the creation of free ______.
In intrinsic semiconductors, the number of free electrons, ne, is equal to the number of ______, nh.
In intrinsic semiconductors, the number of free electrons, ne, is equal to the number of ______, nh.
In p-type semiconductors, the majority charge carriers are called ______.
In p-type semiconductors, the majority charge carriers are called ______.
Dopants in semiconductors create additional energy states, which can be classified as donor levels for n-type and ______ levels for p-type.
Dopants in semiconductors create additional energy states, which can be classified as donor levels for n-type and ______ levels for p-type.
The abundance of majority carriers in extrinsic semiconductors helps to reduce the intrinsic concentration of ______.
The abundance of majority carriers in extrinsic semiconductors helps to reduce the intrinsic concentration of ______.
In n-type semiconductors, electrons come from the donor impurities, which are typically found just below the conduction band at the energy level ______.
In n-type semiconductors, electrons come from the donor impurities, which are typically found just below the conduction band at the energy level ______.
The overall charge neutrality in a semiconductor is maintained because the additional charge carriers are equal in charge and opposite to the ionised ______.
The overall charge neutrality in a semiconductor is maintained because the additional charge carriers are equal in charge and opposite to the ionised ______.
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Study Notes
Semiconductor Fundamentals
- Silicon (Si) and Germanium (Ge) exhibit a diamond-like crystal structure characterized by intact covalent bonds, particularly at low temperatures.
- Increasing temperature supplies thermal energy, allowing some electrons to break free from their bonds, contributing to electrical conduction.
- Free electrons are accompanied by vacancies, termed holes, which carry an effective positive charge, behaving as mobile positive carriers.
Intrinsic and Extrinsic Semiconductors
- In intrinsic semiconductors, the number of free electrons (ne) equals the number of holes (nh), denoted by the intrinsic carrier concentration (ni).
- For p-type semiconductors, the relation shows a predominance of holes over electrons: nh >> ne.
- Charge neutrality is maintained in crystals; total charge from additional carriers equals the charge of ionized lattice cores.
Doping and Its Effects
- Doping introduces additional majority carriers, reducing the intrinsic concentration of minority carriers.
- In n-type semiconductors, donor energy levels (ED) lie just below the conduction band (EC), allowing electrons to transition to EC easily upon ionization.
- Majority carriers are generated from the dopants—pentavalent atoms produce electrons, while trivalent atoms create holes.
Energy Band Gaps
- Carbon, silicon, and germanium have four valence electrons characterized by distinct energy band gaps:
- (Eg)C > (Eg)Si > (Eg)Ge.
- This order indicates the variability in conductivity and energy requirements for excitation in these materials.
p-n Junction Dynamics
- In unbiased p-n junctions, holes diffuse from the p-region to the n-region due to higher hole concentration in the p-region.
- Factors contributing to hole diffusion include attraction from free electrons in the n-region and potential differences across the junction.
- When forward bias is applied to a p-n junction, it lowers the potential barrier, facilitating current flow.
Rectification and Frequency Output
- In half-wave rectification, the output frequency is equal to the input frequency; thus, a 50 Hz input results in a 50 Hz output.
- Full-wave rectification doubles the output frequency compared to the input, achieving an output of 100 Hz for a 50 Hz input.
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