Why silicon is not used in lasers?
Silicon, the material par excellence for electronics, is not used for light sources because of the lack of efficient light emitters and lasers.
Why silicon is not used to fabricate LED or laser diode?
Since Silicon is an Indirect Band Gap semiconductor so electron cannot fall directly to the valence band but must undergo a momentum change as well as a change in energy. So, energy is released as heat along with the light. Hence, silicon is not suitable for the fabrication of LEDs.
What type of semiconductors are preferred in lasers?
The material which often used in semiconductor laser is the gallium Arsenide, therefore semiconductor laser is sometimes known as Gallium Arsenide Laser.
Why germanium is not used in LED?
LEDs are p-n junction devices constructed of gallium arsenide (GaAs), gallium arsenide phosphide (GaAsP), or gallium phosphide (GaP). Silicon and germanium are not suitable because those junctions produce heat and no appreciable IR or visible light. An exposed semiconductor surface can then emit light.
What is the LEDs of SI?
A light-emitting diode (LED) is a semiconductor light source that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons.
How do we protect LED from reverse voltage?
LEDs should be protected with a polarity protection diode if reverse bias voltages are likely. Typical LEDs have about 2 Volts across them when lit but this varies from 1.6 to 3.5 Volts (depending on the colour and type of LED).
What happens if an LED is applied with reverse voltage?
LEDs can be operated on an alternating current voltage, but they will only light with positive voltage, causing the LED to turn on and off at the frequency of the AC supply. Most LEDs have low reverse breakdown voltage ratings, so they will also be damaged by an applied reverse voltage above this threshold.
What is reverse voltage on a LED?
There is a reverse breakdown voltage that allows the LED to conduct (and which can damage it beyond use) and that is only around 5V. LEDs only emit light when they are forward biased, and yes, there is a forward voltage drop. This is never called the ‘reverse voltage’ or the ‘backward voltage’.
What is the maximum reverse voltage for an LED?
Note also that the diode has a peak inverse voltage – There is normally no current flowing through a diode in reverse. The Light Emitting Diode (LED) is made of a different material. Its forward voltage drop is 2v, & the maximum current is about 50 mA.
Can reverse polarity damage LED lights?
LED connection polarity must be strictly observed! If LEDs are reverse-connected to a sufficiently low voltage supply it is possible that they will simply conduct no current, emit no light and suffer no damage. In such cases correcting the polarity will result in correct LED operation with no adverse effects.
What is the breakdown voltage of LED Mcq?
Explanation: The reverse breakdown voltages of LEDs are very low, typically around 5 V. So, if access voltage is provided, they will get fused.
What is the typical forward voltage drop of the yellow Colour led?
This is a very basic 5mm LED with a yellow lens. It has a typical forward voltage of 2.0V and a rated forward current of 20mA.
How much voltage does a green LED need?
Standard red, green, and yellow LEDs have forward voltages in the range 1.4V to 2.6V, depending on the desired brightness and the choice of forward current.
Which LED has largest energy gap?
As listed in Table 1, the color the LED emits depends on the wavelength of the photons emitted from recombination….Band Gap and Photon Wavelength Relation.
| LED color | Wavelength Range (nm) | Semiconductors Used |
|---|---|---|
| Red | 625-760 | AlGaAs |
| Orange | 600-625 | GaAsP |
| Yellow | 577-600 | AlGaInP |
| Green | 492-577 | GaN |
Do I need a resistor for a 12v LED?
If an l.e.d. is to be used with a 12V supply it has to have a current limiting resistor in series with it. No. LEDs sold as 12v, already have a resistor.
Will a 9v battery power a 12v LED?
you can use 9v battery for 12v Led . Just only the brightness is less than 12v battery .
How many LEDs can a 12v battery power?
If you wire a whole bunch of LEDs in parallel rather than dividing the power supplied to them between them, they all share it. So, a 12V battery wired to four 3V LEDs in series would distribute 3V to each of the LEDs.
Can LED lights run on 12v?
Most LED lights are arranged so that they can run off of a 12v battery—in fact, 12v lights can cause a short when plugged directly into a socket, which usually have 110v current. This can be very dangerous, and so the best solution is to run these lights through a relay instead.
How long will a 12-volt battery run a LED light?
A 58.8 AH car battery with a direct DC connection to the light bulb (no inverter) and only discharging down to 50% should be able to power a single 12-volt, 3-watt LED light bulb for 117.6 hours and still be able to start the car.