Semiconductors are materials whose properties are somewhere between those of conductors and insulators, the most common elemental semiconductors are silicon (Si) and germanium (Ge). Silicon is the second most abundant element on Earth after oxygen. Most are found in soil and rocks, but silicon is also found in natural water, trees and plants. The outer electron shell of a silicon atom contains four electrons that can form a perfect covalent bond with four other atoms, forming a tetrahedral crystal lattice structure.
It aims to modify its conductivity by introducing impurities into the semiconductor crystal. The two main impurities in silicon are phosphorus (5 electrons in the outer shell) and boron (3 electrons in the outer shell).
By doping, n-type and p-type semiconductors can be created. Importantly, they remain electrically neutral, the terms only refer to the majority charge carriers. In the n-type, free electrons are the majority carriers, capable of moving through the material. In p-type semiconductors, it is the holes, representing electron deficiencies, that move, creating the effect of a positive charge flow. Individually, the two types of materials have limited functionality, however, when combined, they form the basis of various electronic devices.
The depletion region is formed at the contact between n-type and p-type semiconductors. When the two are connected, free electrons flow from the n-type layer to the p-type layer, forming holes. The process leads to the formation of a zone that plays an important role in the operation of semiconductor devices.
Non-elemental semiconductors, such as gallium nitride (GaN) and gallium arsenide (GaAs), complement the possibilities offered by elemental semiconductors and offer advantages in conductivity, energy efficiency and flexibility. These materials enable the development of miniaturised, high-performance devices. For example, GaN-based chargers are usually included in the box for many smartphones instead of Si-based.