Conductivity

Definition

Conductivity is the ability of a material to conduct electric current, which is influenced by the movement of charge carriers such as electrons and holes. In solid-state physics, conductivity provides insights into how well a material can transport charge, and it is closely related to concepts like effective mass and doping, which modify the behavior and density of charge carriers within a semiconductor or conductor.

5 Must Know Facts For Your Next Test

1. Conductivity can be expressed mathematically as $$ ext{σ} = nq ext{μ}$$, where $$n$$ is the carrier density, $$q$$ is the charge of the carrier, and $$μ$$ is the mobility.
2. Effective mass plays a crucial role in determining the mobility of charge carriers; lighter effective masses generally lead to higher mobility and thus greater conductivity.
3. In n-type semiconductors, extra electrons from donor atoms contribute to increased conductivity compared to intrinsic semiconductors.
4. Conversely, p-type doping introduces holes as majority carriers, which also increases conductivity by allowing for easier movement of charge through the lattice.
5. Temperature affects conductivity; typically, as temperature increases, conductivity increases in metals but decreases in semiconductors due to increased scattering of charge carriers.

Review Questions

• How does effective mass influence the conductivity of a semiconductor?
  • Effective mass influences conductivity by affecting the mobility of charge carriers. A lower effective mass results in higher mobility for electrons or holes, leading to increased conductivity. Therefore, materials with favorable effective mass properties can transport charges more efficiently, contributing positively to their overall electrical performance.
• Discuss how n-type and p-type doping differ in their impact on the conductivity of semiconductors.
  • N-type doping increases conductivity by adding extra electrons to the material from donor atoms, creating more available negative charge carriers. On the other hand, p-type doping introduces holes from acceptor atoms, enhancing positive charge carrier density. Both types of doping effectively increase the overall conductivity, but they do so through different mechanisms involving the addition of either electrons or holes as majority carriers.
• Evaluate how changes in temperature affect the conductivity of metals versus semiconductors, and explain why these differences occur.
  • In metals, increasing temperature typically leads to decreased conductivity due to increased lattice vibrations causing more scattering of free electrons. Conversely, in semiconductors, higher temperatures generally increase conductivity because more electrons gain enough energy to jump from the valence band to the conduction band, increasing carrier density. This contrasting behavior arises from the different mechanisms that govern electrical conduction in these materials—free electron scattering in metals versus thermally activated electron promotion in semiconductors.

Related terms

Charge Carrier: Particles, such as electrons or holes, that carry electric charge through a material, contributing to its conductivity.

Doping: The process of intentionally adding impurities to a semiconductor to change its electrical properties and increase its conductivity.

Mobility: A measure of how quickly charge carriers can move through a material in response to an electric field, influencing the overall conductivity.