n-type Semiconductor

An n-type semiconductor is a group IV intrinsic semiconductor such as silicon (Si) doped with group V elements such as phosphorus (P), arsenic (As), or antimony (Sb) as an impurity.

Group IV elements are tetravalent elements with four valence electrons, while group V elements are pentavalent elements with five valence electrons. A single crystal made only of tetravalent elements such as Si is bound to other elements by covalent bonds, and has no excess electrons or holes. This state without impurities is an intrinsic semiconductor. When a small amount of phosphorus is added to this single crystal (diffusion/doping), one of the valence electrons of the phosphorus becomes an excess electron that can move freely (free electron). When a voltage is applied, this free electron is attracted to the positive electrode and moves, causing a current to flow. For this reason, the resistivity of n-type semiconductors (and p-type semiconductors described below) decreases as the impurity concentration increases.

Si and impurities such as P that make up n-type semiconductors are electrically neutral as single atoms. Therefore, n-type semiconductors are also electrically neutral. However, in n-type semiconductors, the particles (carriers) that carry the charge are free electrons. These carriers have a negative charge, which is why they are called n-type.