Light Emitting Diode Pdf Lecture Notes

The electrons and holes which are already existing in the confining layer combine and emit radiation. Ionization of carriers from the localized levels near the bottom of the conduction band provides electron carriers in the conduction band. As the p- side is lightly doped, much fewer number of holes cross over to the n-side than the number of electrons which diffuse to the n-side. Therefore, free electrons in the conduction band need to lose energy in order to recombine with the holes in the valence band. If is the number of electrons injected into the depletion layer every second, the power output of the device is given by where is the forward current and the electronic charge.

Lecture - Light Emitting Diode (LED) Notes

As a result, low energy photons are released. The process of emitting light in response to the strong electric field or flow of electric current is called electroluminescence. The valence electrons which breaks bonding with the parent atom are called free electrons.

Grouping the range of energy levels of all the valence electrons is called valence band. The emitted photon is no reabsorbed by the material as the band gap on either side of the confining layer is large. The active region is also called as depletion region. This region, which is free of carriers, is called depletion region or space charge layer. These high energy photons have high frequency which is visible to human eye.

Light Emitting Diodes (LEDs)

Light emitting diodes consume low energy. Light emitting diodes consume more energy than silicon or germanium diodes to operate. Thus, normal p-n junction diode operates only in forward bias condition.

Light Emitting Diodes (LEDs)

Recombination of electrons and holes also takes place non-radiatively, which reduce output of the device. The p-type semiconductor and the n-type semiconductor are separated by a depletion region or depletion layer. Recombination of charge carriers takes place only under forward bias condition. Various dopants are added to a p-n junction of GaAs to get emission over a wide range of colours.

The free electrons in the conduction band do not stay for long period. The energy of holes in the valence band is given by Read More. Light emitting diodes emit either visible light or invisible infrared light when forward biased. The electrons which jump from higher energy level to lower energy level will releases energy in the form of a photon or light.

In the similar way, energy level of all the free electrons is almost same. Depletion layer or region Depletion region is a region present between the p-type and n-type semiconductor where no mobile charge carriers free electrons and holes are present. The three semiconductor layers deposited on the substrate are n-type semiconductor, p-type semiconductor and active region. Thus, free electrons recombine with holes in the depletion region.

As a result, more charge carriers will cross the p-n junction. Since the Fermi level for a system in equilibrium must be uniform, band bending takes place. However, they remain confined to this layer as in going over to the layer on the right they find a further potential barrier.

Lecture - Light Emitting Diode (LED)Light Emitting Diode (LED) - Working Construction and Symbol - Diode

The energy lose of free electrons or the intensity of emitted light is depends on the forbidden gap or energy gap between conduction band and valence band. When a forward bias is applied, the hight of the barrier is reduced at both the junctions. It may be recalled that if the effective masses of the electrons and holes are taken to be equal, the intrinsic Fermi level lies in the middle of the gap.

It may be recalled that a p- type semiconductor is made by doping an intrinsic semiconductor with acceptor impurities while an n- type is made by doping with donor impurities. Depletion region is a region present between the p-type and n-type semiconductor where no mobile charge carriers free electrons and holes are present. More the forward current, the greater is the emitted output light. In a direct bandgap material, the bottom of the conduction band lies directly above the top of the valence band.

In other words, the wavelength or color of the emitted light depends on the forbidden gap or energy gap of the material. When sufficient current is passed through the filament, it gets heated up and emits light. Similarly, excitation of electrons from near the top of valence band leave holes in the valence band. Thus electrons to the left of the GaAs layer find a potential barrier.

In normal p-n junction diodes, silicon is most widely used because it is less sensitive to the temperature. Every object in the universe is made up of atoms. The n- side gets depleted of electrons and develop net positive charge. The energy of electrons in the conduction band with the zero of energy being at the top of the valence band is where is the wave vector.

It allows electric current when forward biased and does not allow electric current when reverse biased. Electrons are negatively charged, protons are positively charged, and neutrons have no charge. The electrons from the left can climb up the reduced barrier and enter the GaAs layer. This sudden rise in current may destroy the device. Thus, recombination takes place in depletion region as well as in p-type and n-type semiconductor.

They escape to the surface. In some materials, this energy lose is released mostly in the form of heat. Silicon Controlled Rectifier. However, in materials like gallium arsenide and gallium phosphide the emitted photons have sufficient energy to produce intense visible light.

Light is a type of energy that can be released by an atom. In light emitting diodes, how to write an internship report pdf light is produced due to recombination process. In the double heterostructure shown above a layer of p - tye GaAs is sandwitched between a heavily doped n-type AlGaAs and a lightly doped p-type AlGaAs.

Lecture - Light Emitting Diode (LED)