Which semiconductor used in led

Unlike the light bulb in which electrical energy first converts into heat energy, the electrical energy can also be directly converted into light energy. Light is a type of energy that can be released by an atom. Light is made up of many small particles called photons. Photons have energy and momentum but no mass.

Atoms are the basic building blocks of matter. Every object in the universe is made up of atoms. Atoms are made up of small particles such as electrons, protons and neutrons. Electrons are negatively charged, protons are positively charged, and neutrons have no charge. The attractive force between the protons and neutrons makes them stick together to form nucleus. Neutrons have no charge. Hence, the overall charge of the nucleus is positive.

The negatively charged electrons always revolve around the positively charged nucleus because of the electrostatic force of attraction between them. Electrons revolve around the nucleus in different orbits or shells. Each orbit has different energy level. For example, the electrons orbiting very close to the nucleus have low energy whereas the electrons orbiting farther away from the nucleus have high energy.

The electrons in the lower energy level need some additional energy to jump into the higher energy level. This additional energy can be supplied by the outside source. When electrons orbiting the nucleus gains energy from outside source they jump into higher orbit or higher energy level.

The electrons in the higher energy level will not stay for long period. After a short period, the electrons fall back to lower energy level.

The electrons which jump from higher energy level to lower energy level will releases energy in the form of a photon or light. In some materials, this energy lose is released mostly in the form of heat. The electron which loses greater energy will releases a greater energy photon. Light Emitting Diodes LEDs are the most widely used semiconductor diodes among all the different types of semiconductor diodes available today.

Light emitting diodes emit either visible light or invisible infrared light when forward biased. The LEDs which emit invisible infrared light are used for remote controls. A light Emitting Diode LED is an optical semiconductor device that emits light when voltage is applied. In other words, LED is an optical semiconductor device that converts electrical energy into light energy. When Light Emitting Diode LED is forward biased, free electrons in the conduction band recombines with the holes in the valence band and releases energy in the form of light.

The process of emitting light in response to the strong electric field or flow of electric current is called electroluminescence. A normal p-n junction diode allows electric current only in one direction.

It allows electric current when forward biased and does not allow electric current when reverse biased. Thus, normal p-n junction diode operates only in forward bias condition.

Like the normal p-n junction diodes, LEDs also operates only in forward bias condition. To create an LED, the n-type material should be connected to the negative terminal of the battery and p-type material should be connected to the positive terminal of the battery. In other words, the n-type material should be negatively charged and the p-type material should be positively charged. The construction of LED is similar to the normal p-n junction diode except that gallium, phosphorus and arsenic materials are used for construction instead of silicon or germanium materials.

In normal p-n junction diodes, silicon is most widely used because it is less sensitive to the temperature. Also, it allows electric current efficiently without any damage. In some cases, germanium is used for constructing diodes. However, silicon or germanium diodes do not emit energy in the form of light. Instead, they emit energy in the form of heat. After it was successfully demonstrated in that ruby could be used as a source of laser, inspired researchers sought to produce laser beams using the electroluminescence effect of semiconductors.

At the time, compound semiconductors based on gallium arsenide GaAs and other materials were attracting greater attention than silicon-based semiconductors. Since GaAs is superior to silicon in terms of electric properties at high frequencies, it was considered to be suitable for laser applications, too. After a fierce competition among researchers, three American teams separately conducted successful experiments on LEDs in Band-to-band recombination is the main mechanism that describes carrier activity within an LED.

When an electron in the conduction band meets a hole in the valence band it falls to a lower energy level valence band and releases energy in the form of a photon. The electron drops from band-to-band. When an LED is forward biased, the bands bend slightly in a way to decrease the energy barrier between the n- and p-type semiconductors. This reduced energy barrier enables more of the majority carriers to diffuse to the opposite side of the junction.

Since the electrons from the n- side become the minority once they reach the p- side, recombination is more likely to occur. On the right half of Figure 2 is the n-type semiconductor, shown with electrons black dots being the majority carriers. Forward biasing causes the single Fermi level under equilibrium conditions to split into two quasi-Fermi levels Fp and Fn.

These energy levels are shown as the solid lines near the valence and conduction bands for the p- and n-type semiconductors respectively. The large arrow near the majority electrons represents the direction electrons diffuse across the depletion region. The electrons are represented by the black dots and the holes are the circles.

As an electron from the n-type semiconductor passes the depletion region represented by the diagonal lines it recombines with a hole in the valence band. This results in the electron losing its energy and falling to the valence band where the hole was, represented by the circle with an 'x. When an electron in the conduction band recombines it prefers to go to the highest energy state the peak in the valence band because according to semiconductor band gap theory that is where most of the holes are.

In direct band gap semiconductors like gallium nitride most of these electrons are in the trough of the conduction band and may move to the valence band without any change in momentum from a phonon. The energy versus momentum plots of Figure 3 show that for an electron to recombine in an indirect semiconductor silicon for example additional momentum is required in the form of a phonon. The involvement of a phonon is not likely to occur.

When materials were improved, other advances in the technology followed: methods for connecting the devices electronically, enlarging the diodes, making them brighter, and generating more colors.

To keep them from escaping into the pressurized gas in the chamber, they are often covered with a layer of liquid boron oxide. Next, a rod is dipped into the solution and pulled out slowly. The solution cools and crystallizes on the end of the rod as it is lifted out of the chamber, forming a long, cylindrical crystal ingot. The ingot is then sliced into wafers. Sudden widespread market acceptance in the s was the result of the reduction in production costs and also of clever marketing, which made products with LED displays such as watches seem "high tech" and, therefore, desirable.

Manufacturers were able to produce many LEDs in a row to create a variety of displays for use on clocks, scientific instruments, and computer card readers. The technology is still developing today as manufacturers seek ways to make the devices more efficiently, less expensively, and in more colors.

Diodes, in general, are made of very thin layers of semiconductor material; one layer will have an excess of electrons, while the next will have a deficit of electrons. This difference causes electrons to move from one layer to another, thereby generating light. Manufacturers can now make these layers as thin as. Impurities within the semiconductor are used to create the required electron density. A semiconductor is a crystalline material that conducts electricity only when there is a high density of impurities in it.

The slice, or wafer, of semiconductor is a single uniform crystal, and the impurities are introduced later during the manufacturing process. Think of the wafer as a cake that is mixed and baked in a prescribed manner, and impurities as nuts suspended in the cake. The different semiconductor materials called substrates and different impurities result in different colors of light from the LED. Impurities, the nuts in the cake, are introduced later in the manufacturing process; unlike imperfections, they are introduced deliberately to make the LED function correctly.

This process is called doping. The impurities commonly added are zinc or nitrogen, but silicon, germanium, and tellurium have also been used. As mentioned previously, they will cause the semiconductor to conduct electricity and will make the LED function as an electronic device. It is through the impurities that a layer with an excess or a deficit of electrons can be created. To complete the device, it is necessary to bring electricity to it and from it.

Thus, wires must be attached onto the substrate. These wires must stick well to the semiconductor and be strong enough to withstand subsequent One way to add the necessary impurities to the semiconductor crystal is to grow additional layers of crystal onto the wafer surface. In this process, known as "Liquid Phase Epitaxy," the wafer is put on a graphite slide and passed underneath reservoirs of molten GaAsP.

Contact patterns are exposed on the wafer's surface using photoresist, after which the wafers are put into a heated vacuum chamber. Here, molten metal is evaporated onto the contact pattern on the wafer surface. Gold and silver compounds are most commonly used for this purpose, because they form a chemical bond with the gallium at the surface of the wafer.

LEDs are encased in transparent plastic, rather like the lucite paperweights that have objects suspended in them. The plastic can be any of a number of varieties, and its exact optical properties will determine what the output of the LED looks like. Some plastics are diffusive, which means the light will scatter in many directions. Some are transparent, and can be shaped into lenses that will direct the light straight out from the LED in a narrow beam.

The plastics can be tinted, which will change the color of the LED by allowing more or less of light of a particular color to pass through. Several features of the LED need to be considered in its design, since it is both an electronic and an optic device.

Desirable optical properties such as color, brightness, and efficiency must be optimized without an unreasonable electrical or physical design. These properties are affected by the size of the diode, the exact semiconductor materials used to make it, the thickness of the diode layers, and the type and amount of impurities used to "dope" the semiconductor.

LPE creates an exceptionally uniform layer of material, which makes it a preferred growth and doping technique.