Unsa ang Pamaagi sa Pag-obra sa LED?

Asa ang LED Nagtrabaho?

Pahayag sa LED

Ang LED o Light Emitting Diode, gipahayag kini isip usa ka semiconductor device nga mobati og lihok kapag naa'y elektrisidad nga gitugotan pinaagi sa proseso nga gilaum nga electroluminescence.

Paunsa ang LED nagtrabaho

Tulad sa ordinaryong diode, ang LED diode nagtrabaho kapag forward biased. Sa kasong ini, ang n-type semiconductor adunay mas daghan nga dopant kontra sa p-type pormando ang p-n junction. Kapag forward biased, ang potential barrier gibawas ug ang mga electrons ug holes magcombine sa depletion layer (o active layer), ang light o photons mobati o radiate sa tanang direksyon. Ang typical figure blow showing light emission due electron-hole pair combining on forward biasing.

Ang pagbati sa photons sa LED gi-expalin pinaagi sa energy band theory sa solids, nga magpakita nga ang light emission depende sa material’s band gap nga direct o indirect. Ang mga semiconductor materials nga may direct band gap mao ang mga iya nga mobati og photons. Sa direct bandgap material, ang bottom sa energy level sa conduction band nahimutang diretso sa itaas sa topmost energy level sa valence band sa Energy vs Momentum (wave vector ‘k’) diagram.

Kapag ang electrons ug hole magcombine, ang energy E = hν corresponding sa energy gap △ (eV) mobati sa form sa light energy o photons kung diin ang h mao ang Planck’s constant ug ν mao ang frequency sa light.

Direct Band Gap

Ang indirect band gap materials wala mobati og light, tungod kay ang bottom sa kanilang conduction band dili aligned sa top sa valence band, converting most energy into heat. Examples are Si, Ge etc.

Indirect Band Gap

Example of material which has direct band gap is Gallium Arsenide(GaAs), a compound semiconductor which is the material used in LEDs. Dopant atoms are added to GaAs to give out a wide range of colors. Some of the materials used in LEDs are:

• Aluminium Gallium Arsenide(AlGaAs) – infrared.

• Gallium Arsenic Phosphide(GaAsP) – red, orange, yellow.

• Aluminium Gallium Phosphide(AlGaP) – green.

• Indium gallium nitride (InGaN) – blue, blue-green, near UV.

• Zinc Selenide(ZnSe) – blue.

Physical Structure of LED

Ang LED structured in such a way so that light emitted does not get reabsorbed into the material. So it is ensured that the electron-hole recombination takes place on the surface.

Ang above figure shows the two different ways of structuring LED p-n junction. The p-type layer is made thin and is grown on the n-type substrate. Metal electrodes attached on either side of the p-n junction serve as nodes for external electrical connection. The Light emitting diode p-n junction is encased in a dome-shaped transparent case so that light is emitted uniformly in all directions and minimum internal reflection to take place.

The larger leg of LED represents the positive electrode or anode.

LEDs with more than 2 legs are also available such as 3, 4 and 6 pin configurations to obtain multi-colors in the same LED package. Surface mounted LED displays are available that can be mounted on the PCBs.

LEDs typically require a current of a few tens of milliamps and need high resistance in series due to their higher forward voltage drop of 1.5 to 3.5 volts, compared to ordinary diodes.

White Light LEDs or White LED Lamps

Ang LED lamps, bulbs, street lighting are becoming very popular these days because of the very high efficiency of LEDs in terms of light output per unit input power(in milliWatts), as compared to the incandescent bulbs. So for general purpose lightings, white light is preferred. To produce white light with the help of LEDs, two methods are used :

Mixing of three primary colors RGB to produce white light. This method has high quantum efficiency.

The other method is coating an LED of one color with phosphor of a different color in order to produce white light. This method is commercially popular to manufacture LED bulbs and lightings.

Applications of LEDs

Electronic displays such as OLEDs, micro-LEDs, quantum dots etc.

• As an LED indicator.

• In remote controls.

• Lightings.

• Opto-isolators.