Donor impurities

Definition

Donor impurities are specific types of atoms introduced into a semiconductor material to create additional free charge carriers, typically electrons. These impurities, often from group V elements like phosphorus or arsenic, occupy lattice sites in the semiconductor and provide extra electrons, which enhances the material's conductivity. This process of adding donor impurities is essential for creating n-type semiconductors and plays a crucial role in forming semiconductor junctions, which are fundamental for devices such as diodes and transistors.

5 Must Know Facts For Your Next Test

1. Donor impurities introduce extra electrons into the conduction band of the semiconductor, effectively increasing its electrical conductivity.
2. Common donor impurities include elements like phosphorus (P) and arsenic (As), which have five valence electrons compared to silicon's four.
3. The process of doping with donor impurities is a controlled and precise technique that enables the customization of semiconductor properties for specific applications.
4. In n-type semiconductors, the majority carriers are electrons provided by donor impurities, while holes become the minority carriers.
5. The concentration of donor impurities directly affects the level of conductivity in the semiconductor, with higher concentrations leading to greater electron availability.

Review Questions

• How do donor impurities affect the conductivity of a semiconductor?
  • Donor impurities enhance the conductivity of a semiconductor by introducing additional free electrons into its structure. When these donor atoms are incorporated into the lattice, they provide extra electrons that can move freely within the material. This increase in available charge carriers allows for improved electrical conduction, making n-type semiconductors particularly effective for various electronic applications.
• Compare and contrast n-type and p-type semiconductors in terms of their charge carriers and doping mechanisms.
  • N-type semiconductors are created by doping with donor impurities, which provide excess electrons as majority carriers. In contrast, p-type semiconductors are formed by doping with acceptor impurities that create holes, resulting in positive charge carriers as majority carriers. While n-type relies on additional electrons for conductivity, p-type depends on the movement of holes. Together, these two types of semiconductors form crucial junctions used in various electronic devices.
• Evaluate the impact of varying concentrations of donor impurities on semiconductor performance and device functionality.
  • Varying concentrations of donor impurities significantly impact semiconductor performance and device functionality. Higher concentrations lead to increased electron availability, enhancing conductivity and reducing resistance, which is vital for high-speed electronic devices. However, if impurity levels exceed certain thresholds, it may result in carrier recombination or reduced mobility, negatively affecting performance. Therefore, careful control over doping levels is crucial to optimize device characteristics while ensuring reliable operation.

Related terms

n-type semiconductor:

A type of semiconductor that has been doped with donor impurities to increase the number of free electrons, allowing for enhanced electrical conductivity.

p-type semiconductor:

A type of semiconductor that has been doped with acceptor impurities to create holes, leading to an increase in positive charge carriers.

band gap: The energy difference between the valence band and the conduction band in a semiconductor, which determines its electrical conductivity and optical properties.