Semiconductor is a type of material whose electric conductivity lies between that of a good conductor, like copper, and an insulator, like glass. Its ability to conduct electricity is not fixed but can be controlled by factors such as temperature, impurities (doping), or applied voltage. The most common semiconductors are silicon and germanium, which form the foundation of modern electronics. In a pure state, semiconductors have very few charge carriers, but when doped with certain elements, they can create either an excess of electrons (n-type) or an excess of holes, which are electron vacancies (p-type). This controllable behavior makes semiconductors ideal for creating components like diodes, transistors, and integrated circuits, which are essential in devices ranging from smartphones and computers to solar panels and LEDs. Semiconductors are generally classified into two main types based on their purity and the way their electrical properties are modified.
Intrinsic Semiconductors - These are pure semiconductors that contain no impurities. Their electrical properties are determined by the material itself. At
absolute zero temperature, they act as insulators. However, as the temperature rises, some electrons gain enough
thermal energy to break free from their atoms, leaving behind "
holes" (the absence of an electron). Both free electrons and holes can carry a
current, and the number of free electrons is always equal to the number of holes. Silicon (Si) and germanium (Ge) are common examples of intrinsic semiconductors.
Extrinsic Semiconductors - These are semiconductors that have been intentionally "doped" with impurities to alter their electrical properties and increase their conductivity. Doping involves adding a small, controlled amount of another element to the pure semiconductor material. Based on the type of impurity added, there are two subtypes:
N-type Semiconductors - An n-type semiconductor is created by doping a pure semiconductor with a pentavalent impurity (an element with five valence electrons), such as phosphorus or arsenic. Four of the dopant's valence electrons form covalent bonds with the host atoms, and the fifth electron is left free. This extra, free electron is a negative charge carrier, hence the "n-type" name. In these materials, electrons are the majority carriers, while holes are the minority carriers.
P-type Semiconductors - A p-type semiconductor is created by doping a pure semiconductor with a trivalent impurity (an element with three valence electrons), such as boron or gallium. These three electrons form covalent bonds with three of the four available host atoms, leaving a missing electron or "hole" in the fourth position. This hole is a positive charge carrier, giving the material its "p-type" name. In these materials, holes are the majority carriers, and electrons are the minority carriers.
