Advanced Placement (AP) Chemistry Practice Exam

Which of the following describes n-doping?

1. Addition of an impurity that creates a hole

2. Addition of a substance with more valence electrons

3. A process that removes electrons from the lattice

4. A method to increase the electronegativity

The correct answer is: Addition of a substance with more valence electrons

N-doping refers to the process of introducing impurities into a semiconductor material to increase its electron concentration. When an impurity is added to the semiconductor, specifically an element that has more valence electrons than the semiconductor's base material (like adding phosphorus to silicon), it donates extra electrons to the conduction band. In the context of semiconductors, the base material, typically silicon, has four valence electrons. By adding a dopant with five valence electrons (such as phosphorus), the fifth electron becomes free to move, contributing to electrical conductivity. This enhances the n-type character of the semiconductor because it leads to an increase in the number of free electrons available for conduction. This process is critical in the development of electronic devices, as it allows for better control over the electrical properties of semiconductors, facilitating their use in transistors, diodes, and other electronic components.