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LED & ITS APPLICATION
by
SUDIP KONAR
The theory behind Light Emitting Diodes and their applications The evolution of human
society can be evaluated based on the lighting methods being discovered and invented
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Since then, humans are on a progressive
journey towards higher living standard
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In the current human society, long
after light bulbs have been exploited to their maximum usage, energy consumption due to
traditional light bulbs in homes and offices is becoming an increasingly severe problem faced by
all countries over the world
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An LED is a semiconductor diode
(an electronic device that restricts current flow chiefly to one direction) that converts applied
voltage to light
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The
purpose of this document is to introduce the mechanism behind LEDs and the promising
applications of LEDs in the future
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My intended
audiences are college students who are interested in semiconductor devices and have the basic
knowledge in device physics
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A p-n junction is formed at the boundary between a P-type and N-type
semiconductor created in a single crystal of semiconductor by doping
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Figure 1
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Image adapted from Without external applied voltage Without any
external applied voltage at the two terminals of a p-n junction, an equilibrium condition will
reach in which a potential difference (built-in potential) is formed across the junction
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The electric
field caused by the potential will exert leftward force on holes (conceptual and mathematical
opposite of an electron describing the lack of electron in a position and is represented by red dots
in figure 1) and rightward force on electrons (blue dots in figure 1)
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This unevenness in densities will in turn induce movements of electrons and holes in
the opposite direction to the motions caused by the electric field
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Under forward bias
condition When a positive voltage is applied to the p-region relative to the n-region, the p-n
junction is said to be forward biased and current will flow through the p-n junction structure
under this situation
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In this way, current is generated across the p-n junction
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A p-n junction with forward bias
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com/Electrenicas/Transistors
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One important difference between the
two bands lies in their energy levels
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This implies that electrons in the n-region have higher energies
than holes in the p-region
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As shown in Figure 3 below, the black triangle-shaped component is the symbol for an LED
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When an
electron meets a hole, it will recombine with the hole and fall into the energy level of the hole
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The released energy
happens to be in the form of a photon which is the quantized unit of light
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Since the energy of the photon relates to the photon wavelength and hence photon
color, p-n junctions with various conduction band and valence band energy differences will
produce light of different colors
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Figure 3
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Image adapted from < http://en
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org/wiki/File:PnJunction-LED-E
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That is to say, LEDs can produce more light than can
traditional incandescent light bulbs when consuming the same amount of electricity
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For example, mobile phone
backlighting, flashlights, and displays for calculators and many other electronic devices are
almost dominated by LEDs now
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Despite
all these current applications of LEDs, the lighting methods nowadays in homes and offices are
still the traditional light bulbs due to the relatively high initial cost of LED implementations
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Conclusion The most important mechanisms
behind a LED lie in the transport of electrons and holes in a p-n junction structure, the
recombination process of electrons and holes, and the release of energy in the form of photons
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This fact is becoming more and more important in our current society since
energy conservation has become a global issue
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