Introduction
Over the last 70 years, semiconductors became a crucial element in the manufacturing of electronics. Since the invention of the Transistor, the world of electronics has always been on an exponential curve in terms of research, development, manufacturing, bringing up new devices and technologies. Electronic Devices are all about handling information i.e. high-speed transmission, acquisition and processing in fields of industries and manufacturing, communications, arts, medicine and even in warfare. But all these can be dialed back to the heart of modern electronics and its manufacturing: Semiconductor Devices. Even though an electronic system is manufactured with the help of metals, insulators and semiconductors (more about these later), the semiconductors are considered the backbone of electronics.
What is a Semiconductor?
Before going in to the discussion about different types of Semiconductor Device, it is essential to have an idea about what a semiconductor is. Simply speaking Semiconductors are materials that are neither conductors nor insulators. Expanding a little bit more on this, materials are classified into Conductors, Insulators and Semiconductors based on their ability of conduct electricity. Conductors are materials with very good electricity carrying capacity. Usually metals have good electrical conductivity and you can find Copper or Aluminium in your home’s electrical wiring. On the contrary, Insulators are materials with very bad electrical conductivity. Glass, wood and paper are good examples of Insulators. Now let us talk about the important category of material for our discussion i.e. the semiconductors. At room temperature, Semiconductors are materials with lower electrical conductivity than Conductors but with higher electrical conductivity than Insulators. NOTE: For more detailed understanding about semiconductors, you have to dig deep into the beautifully complicated Quantum Mechanics, which is “certainly” out of scope of this discussion.
Semiconductor Materials
Speaking in terms of electrical conductivity with units of Ω-1 cm-1, semiconductor materials are those with electrical conductivity between 10-9 Ω-1 cm-1 and 102 Ω-1 cm-1. Traditionally, group IV elements like Silicon (Si) and Germanium (Ge) are considered the Elemental Semiconductor Materials i.e. semiconductors with only single atom species. There are other types of semiconductor materials which can be formed by combining elements from group III with that of elements of group V and they are known as Compound Semiconductors. Gallium Arsenide (GaAs) is the best-known semiconductor material in this category and in fact it the second to Silicon as the most commonly used semiconductor material.
What are Semiconductor Devices?
In simple words, Semiconductor devices are a type of electronic components that designed, developed and manufactured based on the Semiconductor materials like Silicon (Si), Germanium (Ge) and Gallium Arsenide (GaAs). Since their use in late 1940’s (or early 1950’s), semiconductors became the main material in the manufacturing of electronics and its variants like optoelectronics and thermoelectronics. Before the usage of semiconductor materials in electronic devices, vacuum tubes were used design of electronic components. The main difference between vacuum tubes and semiconductor devices is that in vacuum tubes, the conduction of electrons occurs in gaseous state while in case of semiconductor device, it happens in “solid state”. Semiconductor devices can be found as both discrete components devices as well as integrated circuits.
Why Semiconductors?
The main reason for using Semiconductor Devices (and hence the underlying Semiconductor Materials) in the manufacturing of electronics devices and components is the ability to easily manipulate its conductivity of charge carriers i.e. electrons and holes. As mentioned earlier, the electrical conductivity of semiconductor materials lies between that of conductors and insulators. Even this conductivity can be further controlled by external or internal factors like electric field, magnetic field, light, temperature and mechanical distortion. Ignoring the external factors like temperature and light for now, a process called Doping is generally performed to the semiconductor materials, where an impurity is introduced into its structure to change the structural as well as electrical properties. A pure semiconductor is known as Intrinsic Semiconductor while an impure or doped semiconductor is known as Extrinsic Semiconductor. When the number of free electrons in the semiconductor structure is increased after doping, the semiconductor is known as n-type semiconductor. Similarly, if the holes are increased, it is known as p-type semiconductor.
Different Types of Semiconductor Devices
The following is a small list of some of the commonly used semiconductor devices. Based on the physical structure of the device, the following list is categorized into Two-terminal Devices and Three-terminal Devices.
Two-terminal Semiconductor Devices
Diode Schottky Diode Light Emitting Diode (LED) DIAC Zener Diode Photo Diode (Photo Transistor) PIN Diode Laser Diode Tunnel Diode Photo Cell Solar Cell Gunn Diode IMPATT Diode TVS Diode (Transient Voltage Suppression Diode) VCSEL (Vertical Cavity Surface Emitting Laser)
Three-terminal Semiconductor Devices
Bipolar Transistor Field Effect Transistor Insulated Gate Bipolar Transistor (IGBT) Darlington Transistor Silicon Controlled Rectifier (SCR) TRIAC Thyristor Unijunction Transistor
There are also a few four-terminal semiconductors like Optocoupler (Photocoupler) and Hall-effect Sensor. For more information on some of the above mentioned semiconductor devices, read “P-N Junction Diode“, “Transistor“, “Thyristor“.
Applications of Semiconductor Devices
As mentioned earlier, semiconductor devices are the basis of almost all electronic devices. Some of the applications of semiconductor devices are:
Transistors are the main components in various integrated circuits like Microprocessors. In fact, they are the main components in the construction of logic gates and other digital circuits. Transistors are also used in analog circuits like amplifiers and oscillators.
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