Advanced Placement (AP) Chemistry Practice Exam

What is the primary role of doping in semiconductors?

1. The removal of impurities from the lattice

2. The addition of an impurity to enhance electrical conductivity

3. The creation of a perfect crystal lattice

4. The conversion of p-type to n-type materials

The correct answer is: The addition of an impurity to enhance electrical conductivity

Doping in semiconductors primarily involves the intentional introduction of specific impurities into a pure semiconductor material, such as silicon, to modify its electrical properties. This process enhances electrical conductivity by introducing additional charge carriers—either electrons or holes—depending on the type of dopant used. When a semiconductor is doped with an n-type dopant (like phosphorus), it introduces extra electrons, thus increasing the number of negative charge carriers. Conversely, when p-type dopants (such as boron) are used, they create holes—regions where electrons are absent—which act as positive charge carriers. This alteration is crucial for the functioning of semiconductor devices, allowing them to conduct electricity more efficiently than the undoped material. The other options do not accurately represent the primary role of doping. For instance, the removal of impurities from the lattice is not a function of doping; rather, it pertains to the purification process of semiconductors. While creating a perfect crystal lattice is an ideal state in crystallography, the nature of doping inherently disrupts this perfection to achieve desired electronic properties. Lastly, converting p-type materials to n-type is not a role of doping but rather a description of types of doping itself. Overall, the addition of an impurity to enhance electrical conductivity