What effect do added impurities have on semiconductor conductivity?

Added impurities can significantly affect the conductivity of a semiconductor. This process is known as doping. Here’s a step-by-step explanation:

1. Intrinsic Semiconductors: Pure semiconductors, such as silicon or germanium, have a certain level of conductivity due to the electrons and holes generated by thermal energy. However, their conductivity is relatively low.

2. Doping: To enhance the conductivity, impurities are intentionally introduced into the semiconductor material. These impurities are called dopants.

3. Types of Dopants:

   • N-type Dopants: These are elements with more valence electrons than the semiconductor material. For example, phosphorus or arsenic (which have five valence electrons) can be added to silicon (which has four valence electrons). The extra electron from the dopant becomes a free charge carrier, increasing the number of free electrons in the material.
   • P-type Dopants: These are elements with fewer valence electrons than the semiconductor material. For example, boron or gallium (which have three valence electrons) can be added to silicon. The absence of a fourth valence electron creates a "hole," which can act as a positive charge carrier.

4. Effect on Conductivity:

   • N-type Semiconductors: The addition of n-type dopants increases the number of free electrons, thereby increasing the material's conductivity.
   • P-type Semiconductors: The addition of p-type dopants increases the number of holes, which also enhances the material's conductivity.

5. Overall Impact: By carefully selecting and controlling the type and amount of dopants, the electrical properties of semiconductors can be precisely tailored for various applications, such as in diodes, transistors, and integrated circuits.

In summary, added impurities (dopants) increase the conductivity of semiconductors by introducing additional charge carriers, either electrons or holes, depending on the type of dopant used.