The main difference between donor and acceptor impurities is that donor impurities increase the conductivity by donating a charge, while acceptor impurities increase the conductivity by accepting a charge.
Donor and acceptor impurities are terms commonly used in the context of semiconductor materials to describe the effects of foreign atoms introduced into the crystal lattice of a semiconductor. These impurities play a crucial role in modifying the electronic properties of the material, particularly its electrical conductivity.
Key Areas Covered
1. What are Donor Impurities
– Definition, Features
2. What are Acceptor Impurities
– Definition, Features
3. Similarities Between Donor and Acceptor Impurities
– Outline of Common Features
4. Difference Between Donor and Acceptor Impurities
– Comparison of Key Differences
Key Terms
Donor Impurities, Acceptor Impurities
What are Donor Impurities
Donor impurities are atoms or ions that have more valence electrons than the host semiconductor material. When donor impurities are introduced into the crystal lattice, they contribute extra electrons to the material’s conduction band. These extra electrons are relatively loosely bound to the impurity atom, allowing them to move freely through the crystal lattice and contribute to the material’s electrical conductivity.
In essence, donor impurities introduce excess electrons, creating negatively charged carriers that enhance the material’s ability to conduct electricity. This process is known as n-type (negative-type) doping.
Phosphorus in silicon is a common donor impurity. Phosphorus has five valence electrons, while silicon has four. When phosphorus is introduced into the silicon lattice, its extra electron becomes a free electron that contributes to the material’s conductivity.
What are Acceptor Impurities
Acceptor impurities are atoms or ions that possess fewer valence electrons than the host semiconductor material. In other words, they have a “hole” in their electron structure, a vacancy that can be thought of as a positive charge carrier. This missing electron in the valence band creates a potential energy level known as an “acceptor level” located just above the valence band. When an electron from the valence band occupies this acceptor level, it leaves behind a hole, which can move through the crystal lattice in response to an electric field.
The process of introducing acceptor impurities into a semiconductor is called “doping.” Doping involves replacing a small fraction of the host semiconductor atoms with acceptor impurity atoms. This intentional introduction of impurities transforms the intrinsic semiconductor material into an extrinsic one, characterized by its altered electronic behavior.
The introduction of acceptor impurities leads to the creation of p-type semiconductors. In a p-type semiconductor, the majority of charge carriers are positively charged holes. These holes can move in response to an electric field, effectively contributing to the material’s electrical conductivity.
Boron is one of the most widely used acceptor impurities in semiconductor materials. With three valence electrons, one less than silicon (Si) which has four, boron creates a vacancy in the crystal lattice when it replaces a silicon atom. This vacancy is effectively a hole that can move through the lattice, creating a positive charge carrier.
Similarities Between Donor and Acceptor Impurities
- Both donor and acceptor impurities are used to intentionally alter the electrical conductivity of semiconductor materials. They introduce additional charge carriers that can contribute to electrical conduction.
- Both types of impurities are introduced into a semiconductor material through a process called “doping.” Doping involves deliberately adding specific atoms or ions to the crystal lattice of the semiconductor.
- Moreover, donor and acceptor impurities create charge carriers in the semiconductor material.
- They affect the energy band structure of the semiconductor material.
- In addition, both types of impurities create charge carriers that contribute to electrical conduction.
Difference Between Donor and Acceptor Impurities
Definition
Donor impurities inject extra electrons into the semiconductor crystal lattice due to having an excess of valence electrons compared to the host material. On the other hand, acceptor impurities generate “holes” or gaps within the valence band of the semiconductor lattice by possessing fewer valence electrons than the host material.
Nature
Donor impurities introduce excess electrons that can move through the material, while acceptor impurities create holes that can also carry a charge.
Energy Bands
While donor impurities introduce energy levels within the band gap near the conduction band, acceptor impurities introduce energy levels near the valence band.
Elements
Elements found in group V of the periodic table commonly function as donor impurities, while elements in group III usually serve as acceptor impurities.
Conclusion
Donor impurities inject extra electrons into the semiconductor crystal lattice due to having an excess of valence electrons compared to the host material. On the other hand, acceptor impurities generate “holes” or gaps within the valence band of the semiconductor lattice by possessing fewer valence electrons than the host material. The main difference between donor and acceptor impurities is that donor impurities increase the conductivity by donating a charge, while acceptor impurities increase the conductivity by accepting a charge.
Reference:
1. “What is Acceptor Impurity.” Farnell.
2. “”
Image Courtesy:
1. “Doped Semiconductor I” By V116408 – Own work (CC BY-SA 3.0) via Commons Wikimedia
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