Extrinsic Semiconductor

Definition

An extrinsic semiconductor is a type of semiconductor material that has been intentionally doped with impurities to enhance its electrical conductivity. This process creates additional charge carriers, either electrons or holes, which significantly alters the material's electrical properties compared to intrinsic semiconductors. Understanding extrinsic semiconductors is crucial for analyzing their behavior in different electronic devices and how they impact carrier concentration, quasi-Fermi levels, current-voltage characteristics, and various current transport mechanisms.

5 Must Know Facts For Your Next Test

1. Extrinsic semiconductors can be classified into n-type and p-type based on the type of dopant used: n-type is doped with elements that provide extra electrons, while p-type is doped with elements that create holes.
2. The level of doping in an extrinsic semiconductor directly affects its electrical conductivity, with higher levels resulting in greater conductivity.
3. At thermal equilibrium, the distribution of electrons and holes can be understood using the concept of quasi-Fermi levels, which represent the energy levels for electrons and holes separately.
4. Current-voltage characteristics of extrinsic semiconductors exhibit different behaviors than intrinsic ones due to the increased carrier concentration and mobility from doping.
5. In extrinsic semiconductors, various current transport mechanisms come into play depending on the concentration of charge carriers and the applied electric field.

Review Questions

• How does doping transform an intrinsic semiconductor into an extrinsic semiconductor, and what are the implications for charge carrier concentration?
  • Doping introduces impurities into an intrinsic semiconductor, effectively changing its properties by increasing the number of available charge carriers. Depending on the type of dopant used, either extra electrons or holes are added to the material. This increase in charge carrier concentration results in enhanced electrical conductivity compared to pure intrinsic semiconductors, allowing them to perform better in electronic applications.
• Discuss how quasi-Fermi levels can be used to describe the behavior of charge carriers in an extrinsic semiconductor under non-equilibrium conditions.
  • Quasi-Fermi levels are essential for understanding how charge carriers behave in an extrinsic semiconductor when external forces like electric fields are applied. These levels separate the energy states for electrons and holes, allowing us to analyze their concentrations independently. When external energy is applied, such as light or voltage, the quasi-Fermi levels shift, indicating changes in carrier distributions and ultimately affecting device performance and response.
• Evaluate the role of extrinsic semiconductors in shaping the current-voltage characteristics of electronic devices and their impact on overall device performance.
  • Extrinsic semiconductors are pivotal in determining the current-voltage characteristics of electronic devices due to their engineered conductivity. The presence of dopants alters how these materials respond under varying voltage levels, leading to distinct I-V curves that illustrate different operational modes like linear or saturation behavior. Understanding this relationship is crucial for designing efficient electronic components such as diodes and transistors, where optimized performance relies heavily on tailored doping strategies.

Related terms

Doping:

The process of adding impurities to a semiconductor to change its electrical properties by increasing the number of free charge carriers.

Intrinsic Semiconductor:

A pure semiconductor without any significant doping, where the electrical conductivity is determined solely by the temperature and intrinsic properties of the material.

Charge Carrier: Particles that carry an electric charge; in semiconductors, these are primarily electrons and holes, which are essential for conducting electricity.