Category: semiconductor Devices

Light Emitting Diode Light Emitting Diodes are directly or indirectly influencing our day-to-day activities. From the message display to LED TVs, everywhere these LEDs exist. It is basically a P-N junction diode that emits light when a forward current is allowed to pass through it. The following figure shows the logic symbol of an LED. How Does a PN Junction Diode Emit Light? LEDs are not made from Silicon or Germanium and elements like Gallium Arsenide (GaAs) and Gallium Phosphide (GaP). These materials are deliberately used as they emit light. Hence, when an LED is forward-biased, as usual electrons cross the junction and unite with holes. This action causes electrons of N-type region to fall out of conduction and return to the valence band. In doing so, the energy possessed by each free electron is then released. A part of released energy emerges as heat and the rest of it is given as visible light energy. If LEDs are made from Silicon and Germanium, then during recombination of electrons, all the energy is dissipated in the form of heat only. On the other hand, materials such as Gallium Arsenide (GaAs) and Gallium Phosphide (GaP) possess enough photons that are sufficient to produce visible light. If LEDs are made from gallium arsenide, they produce red light. If LEDs are made from Gallium Phosphide, then such LEDs emit green light. Now consider two LEDs connected back to back across an external voltage supply source, such that anode of one LED is connected to the cathode of another LED or vice versa. When an external voltage is applied to this circuit, one LED will operate at a time and due to this circuit action, it emits a different light when one LED is forward biased and the other is reverse biased or vice versa. Advantages of LEDs LEDs offer the following advantages − Quite small in size. Very fast switching. Can be operated with very low voltage. A very long life expectancy. Construction procedure permits manufacturing in different shapes and patterns. Applications of LEDs LEDs are mostly used in numeric displays indicating the numbers 0 through 9. They are also used in seven-segment display found in digital meters, clocks, calculators, etc. Learning working make money

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Semiconductor Devices – Introduction It is widely seen that the distance of a nucleus from the electron of a particular atom is not equal. Normally, electrons rotate in a well-defined orbit. A particular number of electrons can only hold by outer shell or orbit. The electrical conductivity of an atom is influenced mainly by the electrons of the outer shell. These electrons have a great deal to do with the electrical conductivity. Conductors and Insulators Electrical conduction is the result of irregular or uncontrolled movement of electrons. These movements cause certain atoms to be good electrical conductors. A material with such type of atoms has many free electrons in its outer shell or orbit. Comparatively, an insulating material has a relatively small number of free electrons. Consequently, the outer shell electrons of insulators tend to hold their place firmly and hardly allow any current to flow through it. Therefore, in an insulating material, very little electrical conductivity takes place. Semiconductors In between conductors and insulators, there is a third classification of atoms (material) known as semiconductors. Generally, the conductivity of a semiconductor lies in between the conductivities of metals and insulators. However, at absolute zero temperature, the semiconductor also acts like a perfect insulator. Silicon and germanium are the most familiar semiconductor elements. Copper oxide, cadmium-sulfide, and gallium arsenide are some other semiconductor compounds that are frequently used. These kinds of material are generally classified as type IVB elements. Such atoms have four valence electrons. If they can give up four valence electrons, stability can be accomplished. It can also be achieved by accepting four electrons. Stability of an Atom The concept of stability of an atom is an important factor in the status of semiconductor materials. The maximum number of electrons in the valence band is 8. When there are exactly 8 electrons in the valence band, it can be said that the atom is stable. In a stable atom, the bonding of valence electrons is very rigid. These types of atoms are excellent insulators. In such atoms, free electrons are not available for electrical conductivity. Examples of stabilized elements are gases such as Argon, Xenon, Neon, and Krypton. Due to their property, these gases cannot be mixed with other material and are generally known as inert gases. If the number of valence electrons in the outer shell is less than 8, then the atom is said to be unstable i.e., the atoms having fewer than 8 valence electrons are unstable. They always try to borrow or donate electrons from the neighboring atoms to become stable. Atoms in the outer shell with 5, 6, or 7 valence electrons tend to borrow electrons from other atoms to seek stability, while atoms with one, two, or three valence electrons tend to release these electrons to other nearby atoms. Learning working make money

Semiconductor Devices Tutorial Job Search The electronic components exploiting the electronic properties of semiconductor materials, are termed as semiconductor devices. This tutorial discusses the functional operation of semiconductor devices, explains the operation of devices in a circuit, etc. Each topic in this tutorial is explained well using circuit diagrams for better understanding. After completing this tutorial, readers will be at a moderate level of expertise to explain the basics related to semiconductor devices. Audience This tutorial will be useful for all those readers who want to gain knowledge on semiconductor devices. Upon completion of this tutorial, you will able to explain the functional operation of semiconductor devices. Prerequisites We don’t assume any prior knowledge of Electronics is necessary to understand this tutorial. The material is meant for beginners and it should be useful for most readers. Learning working make money