A semiconductor is a material whose electrical conductivity falls between that of a conductor, such as copper, and that of an insulator, such as glass. Its resistivity decreases as its temperature rises; metals do the opposite. By introducing impurities (“doping”) into the crystal structure, its conducting properties can be altered in useful ways. A semiconductor junction is formed when two differently doped regions of the same crystal coexist.
Semiconductors are commonly made of silicon (Si), germanium (Ge), gallium arsenide (GaAs), and indium gallium arsenide (InGaAs). The bandgap is a unique property of these materials that determines their electrical behavior. The energy difference between the valence band (where electrons are bound) and the conduction band (where electrons can move freely) is defined as the bandgap.
The electrons in the valence band are bound in an intrinsic semiconductor (pure form), and there are no free electrons in the conduction band. However, the electrical properties of a semiconductor material can be altered when impurities are intentionally added to it, a process known as doping.
The behavior of charge carriers at these junctions, which include electrons, ions, and electron holes, is the foundation of diodes, transistors, and most modern electronics. Silicon, germanium, gallium arsenide, and elements near the periodic table’s “metalloid staircase” are examples of semiconductors. Gallium arsenide, the second-most common semiconductor after silicon, is used in laser diodes, solar cells, microwave-frequency integrated circuits, and other applications. Silicon is a critical component in the fabrication of most electronic circuits.
Doping involves the introduction of impurity atoms that have extra or missing electrons, resulting in two types of doped semiconductors: n-type and p-type. Impurity atoms provide extra electrons in n-type semiconductors, resulting in an excess of negative charge carriers (electrons). Impurity atoms in p-type semiconductors create “holes,” or missing electrons, which act as positive charge carriers.
Semiconductor devices, such as transistors, take advantage of doped semiconductors’ unique properties. Transistors are essential components of electronic circuits that allow for signal amplification, switching, and control. Integrated circuits (ICs) are constructed from a large number of transistors and other components, allowing complex electronic functions to be packed into a small space.
Semiconductor devices can have a variety of useful properties, such as the ability to pass current more easily in one direction than the other, variable resistance, and sensitivity to light or heat. Devices made from semiconductors can be used for amplification, switching, and energy conversion because the electrical properties of a semiconductor material can be modified by doping and the application of electrical fields or light.
Semiconductors have played a critical role in the advancement of technology, enabling the development of computers, smartphones, televisions, and a wide range of electronic devices that have become indispensable in our daily lives. Continuous advances in semiconductor technology have resulted in faster, more efficient devices with increased functionality.
