The capability of a substance to permit electrons to flow through is referred to as its conductivity. A conductor allows electrons to pass through while an insulator will require lots of energy to do the same. A semiconductor is, therefore, a material that has a conductivity between that of conductors such as metals, and non-conductors (insulators) such as ceramics. They can be pure elements like germanium and silicon, or they can be compounds like cadmium arsenide. The conductance of a semiconductor depends on the amount of voltage, current or even visible light applied to it. They are useful materials because the flow of electrons can be controlled, making them suitable in the manufacture of numerous equipment and electronic devices.
In order to change or modulate specific electrical properties of a semiconductor, impurities are added to the element, a process referred to as doping. This is done in order to generate a surplus or deficiency in valence electrons. If the dopant adds electrons to the semiconductor, it becomes an n-type semiconductor and it carries current in form of these negatively charged electrons. If it takes the electrons away, it’s called a p-type semiconductor and it carries current predominantly in form of electron deficiencies called holes. A hole is positively charged, and equal (but opposite) to an electron charge. It also flows in the opposite direction.
Because the conductivity of a semiconductor lies between conductor and insulator, it’s sometimes referred to as an artificial material. A semiconductor can be transformed into the perfect insulator by exposing it to absolute zero temperatures. On increasing the temperature, the electrons in the valence band start absorbing heat energy and get “excited”, jumping into the conduction band. Meaning that its conductivity increases with an increase in temperature. This property, known as Negative Temperature Coefficient (NTC) and commonly used in Silicon and Germanium, makes semiconductors very useful temperature sensors. For example, it’s used in thermostats as transducers to measure changes in temperature and is applicable in numerous industrial and medical equipment for controlling the temperature.
Semiconductors have very intriguing optical properties and applications. Because they contain impurities, they can emit light of a specific color when a specific voltage is applied, making them ideal for manufacturing light-emitting diodes (LEDs) and in making lasers. In some semiconductors, nanometer-scale particles enable them to emit light of different colors depending on their size.
Semiconductors are also used in the fabrication of solar cells because they can generate current from absorbing light. Currently, the most popular cells used today are silicon-based solar cells due to their efficiency and low occurrence of defects. Solar cells made from other kinds of semiconductors are also available but are expensive to produce in large scale. Although Silicon is the most important today, scientists are still searching for a material that can absorb light over a wide range of wavelengths but with low costs of manufacturing.
Today, it’s impossible to imagine life without semiconductors. They are used in microchips, which are ingrained in almost every electronic equipment we have, for instance, computers, mobile phones, TVs, and radios, among others. Their importance is overlooked because they are not sold in stores, but they play a central role in the operational aspects of our lives today, enabling us to live more comfortably than ever.
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