How Crystal Defects Affect Conductivity

Crystal defects, like vacancies, interstitials, and dislocations, can greatly change how well materials conduct electricity. Let’s break down how these defects impact conductivity:

1. Carrier Concentration:

   • Defects can create more charge carriers, which are particles that help electricity flow. For example, in n-type semiconductors, certain impurities can add extra electrons. Sometimes, this can boost the number of electrons by as much as 10%.

2. Scattering Mechanisms:

   • Defects can cause charge carriers to scatter, or bounce around. This makes it harder for them to move freely, which can lower their mobility. For instance, just one dislocation can reduce electron mobility by over 30%. This has a big effect on how well electricity flows.

3. Resistivity Changes:

   • When defects are present, materials usually become less conductive, meaning they resist the flow of electricity more. There’s a simple way to understand this relationship:
   • The resistivity (how much a material resists electricity) can be affected by the number of defects present. The more defects there are, the higher the resistivity.

4. Temperature Dependence:

   • As the temperature goes up, defects can move around more, which might help conductivity. But there's a catch: increased movement (called phonon scattering) usually makes conductivity go down overall.

In short, crystal defects are important because they change how materials conduct electricity. Understanding these changes is crucial, especially when it comes to making semiconductors and materials that conduct electricity well.