Special Purpose Diodes LED, photodiode, laser diode wave shaping circuits using diode

Special Purpose Diodes:1. LEDs2. Photo Diodes3. Laser DiodesA Presentation by:Abhijeet gupta : 140110111001Darshak padsala: 140110111008HireN patel : 140110111035Prerak Trivedi : 140110111045ELECTRONIC DEVICES AND CIRCUITS, GCET

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What Diodes Actually Are?As the name suggests di-ode means a device having two junctions or electrodes.It is usually made up of semiconductors but some are made up of metallic materials too.Diodes can be used as rectifiers, signal limiters, voltage regulators, switches, signal modulators, signal mixers, signal demodulators, and oscillators.

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What Is Opto-Electronics?Before moving on the special purpose diodes, lets understand the term OPTOELCETRONICS.OPTOELECTRONICS is the technology which combines both optics and electronics.This field includes many devices based on the action of PN Junction diode.Few Optoelectronic devices are:LEDs, Photodiode, Optocouplers and Laser Diode.ELECTRONIC DEVICES AND CIRCUITS, GCET

Light Emitting Diodes work on the principle of the emission of specific-frequency radiant energy whenever electrons fall from a higher energy level to a lower energy level. LEDs rule the world of lighting because of their low energy consumption, smaller size, faster switching and long life.Just like an ordinary diode LEDs also have anode and cathode which are properly biased.A General Info About LEDsELECTRONIC DEVICES AND CIRCUITS, GCET

What Are Different Parts Of LED?

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What Is The Basic Circuit Of An LED?

The basic circuit diagram shows a source connected to a resistor and an LED and the outward arrows symbolize the radiated light. In a forward-biased LED, free electrons cross the PN junction and fall into holes. As these electrons fall from a higher to a lower energy level, they radiate energy in the form of photons. In ordinary diodes, this energy is radiated in the form of heat. But in an LED, the energy is radiated as light. This effect is referred to as electroluminescence.ELECTRONIC DEVICES AND CIRCUITS, GCET

How are the colors obtained?The colour of the light, which corresponds to the wavelength energy of the photons, is primarily determined by the energy band gap of the semiconductor materials that are used. By using elements like gallium, arsenic, and phosphorus, a manufacturer can produce LEDs that radiate red, green, yellow, blue, orange, white or infrared (invisible) light. LEDs with various colours have various applications like red, blue etc. are used for decoration and indication whereas infrared are used for security purposes.ELECTRONIC DEVICES AND CIRCUITS, GCET

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LED Voltage and Current

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What Photo Diodes Are? A photodiode is a semiconductor device that converts light into current.Current is generated when photons are absorbed in a photodiode.It contains optical filters, built in lenses and special semiconductor material that is capable of emitting electrons or are photo sensitive.ELECTRONIC DEVICES AND CIRCUITS, GCET

What Is The Construction Of Photo Diode?In the photodiode fabrication process a thick intrinsic layer is inserted between the p-type and n-type layers. The middle layer may be either completely intrinsic or very lightly doped to make it and n- layer. In some instances it may be grown as an epitaxial layer onto the substrate, or alternatively it may be contained within the substrate itself.One of the main requirements of the photodiode is to ensure that the maximum amount of light reaches the intrinsic layer. One of the most efficient ways of achieving this is to place the electrical contacts at the side of the device as shown. ELECTRONIC DEVICES AND CIRCUITS, GCET

What Is The Construction Diagram Of Photo Diode?

This enables the maximum amount of light to reach the active area. It is found that as the substrate is heavily doped, there is very little loss of light due to the fact that this is not the active area.

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On What Principle Does Photo Diode Work? A photodiode is apn junctionorPIN structure. When aphotonof sufficient energy strikes the diode, it creates anelectron-holepair. This mechanism is also known as the innerphotoelectric effect. If the absorption occurs in the junction'sdepletion region, or one diffusion length away from it, these carriers are swept from the junction by the built-in electric field of the depletion region. ELECTRONIC DEVICES AND CIRCUITS, GCET

Thus holes move toward theanode, and electrons toward the cathode, and aphotocurrentis produced. The total current through the photodiode is the sum of the dark current (current that is generated in the absence of light) and the photocurrent, so the dark current must be minimized to maximize the sensitivity of the device.ELECTRONIC DEVICES AND CIRCUITS, GCET

How Does The Photo Diode Work?When photons of energy greater than 1.1 eV hit the diode, electron-hole pairs are created. The intensity of photon absorption depends on the energy of photons the lower the energy of photons, the deeper the absorption is. This process is known as the inner photoelectric effect.If the absorption occurs in the depletion region of the p-n junction, these hole pairs are swept from the junction - due to the built-in electric field of the depletion region. As a result, the holes move toward the anode and the electrons move toward the cathode, thereby producing photocurrent.

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Graph

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Applications Of Photo Diodes CamerasMedical devicesSafety equipmentOptical communication devicesPosition sensorsBar code scannersAutomotive devicesSurveying instruments

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How Laser Diodes Look Like?

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What is Laser Diode?A laser diode, also known as an injection laser or diode laser, is a semiconductor device that produces coherent radiation (in which the waves are all at the same frequency and phase) in the visible or infrared (IR) spectrum when current passes through it.The laser diode is the most common type of laser produced with a wide range of uses that include, but are not limited to, fibre optical communication , barcode readers , laser pointers , laser printing, laser scanning and increasingly directional lighting sources .

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How does it work?When current is passed through semiconductors both negatively charged electron from N type semiconductor and positively charged hole from P-type semiconductor begin to flow towards PN junction.Holes exist at lower energy level than free electrons. So, electron must lose small amount of energy to combine with hole.It combines with hole by releasing single photon of light.Top and bottom surfaces of PN junction is coated with mirrored material to trap photon of light.Photon bounces around inside the PN junction on mirrored top and bottom surfaces.

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Photon encourages other holes and electron to combine and they also release their own photon of light.Photon that are released by other electron and holes are of same polarity, same phase and of same direction of the original photon.The process continue and more photon is produced. Photons will keep increasing in numbers until whole PN junction is filled with laser light.Some of the laser light exists the rear of laser diode and hit photo diode

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The photo diode uses this information to regulate voltage to the laser diode.Vast majority of the light exist through the front of the laser diodeThis diffracted light must be made into typical straight laser beam This is done by passing the light through collimating lens

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Applications of Laser DiodeIn telecommunication as easily modulated and easily coupled light sources for fibre optics communication.In various measuring instruments, such as rangefinders. Another common use is in barcode readers. Visible lasers, typically red but later also green, are common as laser pointers. Both low and high-power diodes are used extensively in the printing industry both as light sources for scanning (input) of images and for very high-speed and high-resolution printing plate (output) manufacturing.

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Infrared and red laser diodes are common in CD players, CD-ROMs and DVD technology. Violet lasers are used in HD DVD and Blu-ray technology. Diode lasers have also found many applications in laser absorption spectrometry (LAS) for high-speed, low-cost assessment or monitoring of the concentration of various species in gas phase. High-power laser diodes are used in industrial applications such as heat treating, cladding, seam welding and for pumping other lasers, such as diode-pumped solid-state lasers.

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