How does an LED work at the molecular AND practical level? | Intermediate Electronics

Have you ever asked yourself how this smallelectronic device, an LED, emits light? Compared to the much less efficient incandescentlight bulb, which produces light by converting electrical energy into heat energy, LEDs directlyconvert electrical energy into light energy.

An LED or Light Emitting Diode is basicallya type of diode that is specifically designed to emit light.

It operates the same way a general-purposeor a rectifier diode operates.

But what makes it emit light is the semiconductormaterial used in it.

The construction of an LED is just the sameas a normal pn junction diode.

However, instead of silicon or germanium, LEDs are made from compound semiconductor materials like gallium arsenide, gallium phosphideand other semiconductor materials that emit light.

Silicon is most widely used in normal diodesbecause it is less sensitive to temperature.

However, it doesn’t release energy in theform of light but in the form of heat so they are not used in LEDs.

So, an LED is a diode, therefore, just likea regular diode, it can be forward biased or reverse biased.

However, an LED only emits light when it isin the forward bias condition.

So for now, let’s just focus on forwardbiasing an LED.

To forward bias an LED, basically you justconnect its cathode terminal to the negative side of an external bias voltage and its anodeterminal to the positive side of the external bias voltage.

When an LED is forward biased, the free electronsfrom the n region gain enough energy to cross the junction and recombine with the holesin the p region.

Initially, free electrons from the n regionare in the conduction band but as they cross over into the p region, they release energyand fall into a hole in the valence band.

For a normal silicon diode, the energy releasedwould be in the form of heat.

But for the semiconductor materials used inLEDs, the energy released when free electrons recombine with holes is in the form of light, a photon.

From the point of view of an energy diagram, we can see that forward biasing an LED narrows the depletion region and allows free electronsto cross the junction.

As free electrons cross the junction and recombinewith holes, electrons release energy in the form of light.

Basically, what happens inside an LED whenit is forward biased is just similar to a regular diode, except that electrons releaselight instead of heat when they change energy levels.

We don’t need to discuss the reverse biasexcept to say it acts like a diode when reverse biased and if you exceed the established parameters, you will destroy the LED.

One of the first LED characteristics thatwe consider when we use an LED is, of course, its color.

Sometimes we use green LEDs to indicate thatthe circuit is in good condition or red LEDs to indicate that there’s a problem.

LEDs can be in color red, orange, yellow, green, blue, white, or violet and what determines the color of an LED is the semiconductor materialused in it.

Photons have different wavelengths based ontheir energy, or energy based on their wavelengths, depending on how you look at it.

So, to achieve different colors, scientistsand engineers have figured out how much energy an electron passing from one material to anotherneeds to lose in order for it to emit the photon of the correct wavelength for the desiredcolor.

We’ve put together a quick table that showsthe colors, their associated wavelengths, and the material currently used to generatethat color.

If you’d like more time to check this tableout, it’s under the references at CircuitBread.

com Using a 5mm LED, you can see how this combinationon a semiconductor level is actually implemented into something useful.

If you try to look at what's inside a 5mmLED, you can see that the lead frame connected to the cathode terminal, also known as anvil, holds the semiconductor material.

The reflective cup which is connected to theanvil actually holds the semiconductor material.

The n region is placed at the bottom so it’sconnected to the cathode terminal while the p region is at the top.

Then there’s just a wire that connects itto post lead frame which is connected to the anode terminal.

One reason for this design is that the majorityof the light produced by an LED is from the area of the junction nearer to the p region.

So this area is kept as close to the surfaceof the device as possible.

And that’s it! I hope this video helps you understand howan LED works.

If you have any questions, leave it in thecomments below and if you’ve found this interesting or helpful, give it a like andsubscribe to our channel! /**************************************ORIGINAL(UNCUT)*********************************************/ Intro Have you ever asked yourself how this smallelectronic device, an LED, emits light? Compared to the much less efficient incandescentlight bulb, which produces light by converting electrical energy into heat energy, LEDs directlyconvert electrical energy into light energy.

Over the last few years, LED usage has increasedexponentially.

This is because LEDs are efficient, easilydimmable, non-toxic, and are much more durable compared to other light sources.

But what is an LED and how does it actuallywork? In this video, we are going to answer thesequestions.

What is an LED? What makes it different from other types ofdiodes? An LED or Light Emitting Diode is basicallya type of diode that is specifically designed to emit light.

It operates the same way a general-purposeor a rectifier diode operates.

But what makes it emit light is the semiconductormaterial used in it.

The construction of an LED is just the sameas a normal pn junction diode.

However, instead of silicon or germanium, LEDs are made from compound semiconductor materials like gallium arsenide, gallium phosphideand other semiconductor materials that emit light.

Silicon is most widely used in normal diodesbecause it is less sensitive to temperature.

However, it doesn’t release energy in theform of light but in the form of heat so they are not used in LEDs.

How does an LED work? So, an LED is a diode, therefore, just likea regular diode, it can be forward biased or reverse biased.

However, an LED only emits light when it isin the forward bias condition.

So for now, let’s just focus on forwardbiasing an LED.

Forward Bias To forward bias an LED, basically you justconnect its cathode terminal to the negative side of an external bias voltage and its anodeterminal to the positive side of the external bias voltage.

But we can’t forget that LEDs, especiallythe low power types, can’t take much current, [at][au][av][aw][ax][ay]so we need to limitthe current flowing through it.

For low power LEDs, we can simply use a resistorto limit the current.

Forward Voltage and Forward Current Speaking of voltage and current, there aretwo basic parameters that we need to consider when working with LEDs, forward voltage andforward current.

For the same reasons as with regular diodes[az], the forward voltage of an LED is the voltage required across an LED in order for it tostart conducting.

Though LEDs require higher forward voltagecompared to general-purpose diodes.

The forward voltage of an LED is dependenton the semiconductor material used but are typically between 1.

6 to 4.

4 volts.

LEDs that are not as bright may require lessvoltage than brighter LEDs since bright LEDs need more power to work.

The forward current of an LED indicates thecurrent that the LED can handle without causing damage.

When you try to read LED datasheets, you willnotice that this parameter is located in the maximum absolute ratings.

Therefore, don’t exceed this limit.

For long term performance, it is recommendedto use drive currents less than the specified forward current of an LED.

So, in order for an LED to work, the externalbias voltage must be greater than the forward voltage of the LED and can at least supplythe forward current.

To avoid any damage to the LED, make surethat you also limit the current flowing through it.

Depending on the power requirements, you mightuse a resistor or a high power LED driver.

[ba][bb] What happens inside an LED when it is forwardbiased? So far what we discussed is just about forwardbiasing an LED and its two basic parameters.

Now let’s discuss what’s happening insidean LED when it is in forward bias condition.

[bc][bd] When an LED is forward biased, the free electronsfrom the n region gain enough energy to cross the junction and recombine with the holesin the p region.

Initially, free electrons from the n regionare in the conduction band but as they cross over into the p region, they release energyand fall into a hole in the valence band.

For a normal silicon diode, the energy releasedwould be in the form of heat.

But for the semiconductor materials used inLEDs, the energy released when free electrons recombine with holes is in the form of light.

[be]From the point of view of an energy diagram, we can see that forward biasing an LED narrowsthe depletion region and allows free electrons to cross the junction.

As free electrons cross the junction and recombinewith holes, electrons release energy in the form of light.

[bf]So that’s it! Basically, what happens inside an LED whenit is forward biased is just similar to a regular diode, except that electrons releaselight instead of heat when they change energy levels.

Reverse Bias We don’t need to discuss the reverse biasexcept to say it acts like a diode when reverse biased and if you exceed the established parameters, you will destroy the LED.

LED Color One of the first LED characteristics thatwe consider when we use an LED is, of course, its color.

Sometimes we use green LEDs to indicate thatthe circuit is in good condition or red LEDs to indicate that there’s a problem.

LEDs can be in color red, orange, yellow, green, blue, white, or violet and what determines the color of an LED is the semiconductor materialused in it.

Photons have different wavelengths based ontheir energy, or energy based on their wavelengths, depending on how you look at it[bg].

So, to achieve different colors, scientistsand engineers have figured out how much energy an electron passing from one material to anotherneeds to lose in order for it to emit the photon of the correct wavelength for the desiredcolor.

We’ve put together a quick table that showsthe colors, their associated wavelengths, and the material currently used to generatethat color.

If you’d like more time to check this tableout, it’s under the references at CircuitBread.

com ColorWavelength Range (nm) Material[bh][bi][bj] Ultraviolet< 400 Aluminium nitride (AlN)Aluminium gallium nitride (AlGaN) Aluminium gallium indium nitride (AlGaInN)[bk][bl][bm] Violet400 – 450 Indium gallium nitride (InGaN)[bn][bo][bp] Blue450 – 500 Indium gallium nitride (InGaN)Silicon carbide (SiC) [bq][bs]Green 500 – 570Gallium phosphide (GaP) Aluminium gallium indium phosphide (AlGaInP)Aluminium gallium phosphide (AlGaP) [bt][bu][bv]Yellow 570 – 590Gallium arsenide phosphide (GaAsP) Aluminium gallium indium phosphide (AlGaInP)Gallium phosphide (GaP) [bw][bx][by]Orange / Amber 590 – 610Gallium arsenide phosphide (GaAsP) Aluminium gallium indium phosphide (AlGaUInP)Gallium phosphide (GaP) [bz][ca][cb]Red 610 – 760Aluminium gallium arsenide (AlGaAs) Gallium arsenide phosphide (GaAsP)Aluminium gallium indium phosphide (AlGaInP) Gallium phosphide (GaP)[cc][cd][ce] Infrared> 760 Gallium arsenide (GaAs)Aluminium gallium arsenide (AlGaAs) [cf][cg][ch] LED Construction Using a 5mm LED, you can see how this combinationon a semiconductor level is actually implemented into something useful.

If you try to look at what's inside a 5mmLED, you can see that the lead[ci][cj][ck][cl][cm][cn] frame connected to the cathode terminal, alsoknown as anvil, holds the semiconductor material.

The reflective cup which is connected to theanvil actually holds the semiconductor material.

The n region is placed at the bottom so it’sconnected to the cathode terminal while the p region is at the top.

Then there’s just a wire that connects itto post lead frame[co][cp][cq] which is connected to the anode terminal.

One reason for this design is that the majorityof the light produced by an LED is from the area of the junction nearer to the p region.

So this area is kept as close to the surfaceof the device as possible.

[cr][cs][ct] Outro/Summary And that’s it! I hope this video helps you understand howan LED works.

If you have any questions, leave it in thecomments below and if you’ve found this interesting or helpful, give it a like andsubscribe to our channel! /**************************************ORIGINAL(UNCUT)*********************************************/ [a]slide-in[b]replace boxes with diode symbol, animation stays basically the same[c]+jb@swellfox.

com we just noticed the bias is backwards on this.

this illustration is depicted as reverse biasedhaha [d]+taylor@swellfox.

com yeah, sorry this isincorrect.

I put the correct image below.

Sorry my mistake.

[e]animate electrons moving from the n regionup to the p region, and then down into a hole in the valence band[f]E={frac {hc}{lambda }} [g]I think we could have a stylized versionof this pop up on the screen at some point, but reference the fact that we have this onour website as a reference material for further perusal.

[h]Ok Josh! I'll ask Stephanie to make a CB version ofthis table.

[i]Thank you![j]I think we could have a stylized version of this pop up on the screen at some point, but reference the fact that we have this on our website as a reference material for furtherperusal.

[k]Ok Josh! I'll ask Stephanie to make a CB version ofthis table.

[l]Thank you![m]I think we could have a stylized version of this pop up on the screen at some point, but reference the fact that we have this on our website as a reference material for furtherperusal.

[n]Ok Josh! I'll ask Stephanie to make a CB version ofthis table.

[o]Thank you![p]I think we could have a stylized version of this pop up on the screen at some point, but reference the fact that we have this on our website as a reference material for furtherperusal.

[q]Ok Josh! I'll ask Stephanie to make a CB version ofthis table.

[r]Thank you![s]I think we could have a stylized version of this pop up on the screen at some point, but reference the fact that we have this on our website as a reference material for furtherperusal.

[t]Ok Josh! I'll ask Stephanie to make a CB version ofthis table.

[u]Thank you![v]I think we could have a stylized version of this pop up on the screen at some point, but reference the fact that we have this on our website as a reference material for furtherperusal.

[w]Ok Josh! I'll ask Stephanie to make a CB version ofthis table.

[x]Thank you![y]I think we could have a stylized version of this pop up on the screen at some point, but reference the fact that we have this on our website as a reference material for furtherperusal.

[z]Ok Josh! I'll ask Stephanie to make a CB version ofthis table.

[aa]Thank you![ab]I think we could have a stylized version of this pop up on the screen at some point, but reference the fact that we have this on our website as a reference material for furtherperusal.

[ac]Ok Josh! I'll ask Stephanie to make a CB version ofthis table.

[ad]Thank you![ae]I think we could have a stylized version of this pop up on the screen at some point, but reference the fact that we have this on our website as a reference material for furtherperusal.

[af]Ok Josh! I'll ask Stephanie to make a CB version ofthis table.

[ag]Thank you![ah]How would you pronounce this word? LEED or LED? I'm assuming LEED but I'm not familiar withthe term "lead frame" and so I could be off base here.

[ai]same as anode lead and cathode lead[aj]So "lead frame" is a thing? I've just never heard of that.

[ak]me neither!but seeing as cathode lead is connected to the lead frame/anvil, I would be super comfortablesaying lead the same way [al]Hi guys! According to wiki https://en.

wikipedia.

org/wiki/Lead_frameand other sites, "Lead frames are the metal structures inside a chip package that carrysignals from the die to the outside.

" https://image.

slidesharecdn.

com/theledrevolution-141118065629-conversion-gate01/95/the-led-revolution-3-638.

jpg?cb=1416293865 Inside an LED, Anvil and Post are the leadframes or internal metal structures that support the semiconductor material.

[am]Okay, so it is what I thought it is, it'sjust not a term I've heard before.

I'm going to tell myself that the word "frame"is because it provides some structural stability inside the LED or something.

That'll help me wrap my head around that term.

[an]Sorry, I'm not sure what this means.

I believe that it's just saying that the wireconnects it to the anode terminal but then I could be skipping a step.

[ao]positive lead frame?positive terminal? [ap]Hi guys! According to wiki https://en.

wikipedia.

org/wiki/Lead_frameand other sites, "Lead frames are the metal structures inside a chip package that carrysignals from the die to the outside.

" https://image.

slidesharecdn.

com/theledrevolution-141118065629-conversion-gate01/95/the-led-revolution-3-638.

jpg?cb=1416293865 Inside an LED, Anvil and Post are the leadframes or internal metal structures that support the semiconductor material.

[aq]Temporary Image.

Stephanie is still working on it.

[ar]I'm buying material to make an LED thesize of the mercury vapor bulb we have [as]That would be an awesome prop and alsoa great office decoration.

[at]Should we assume people know this? I think we can, but there may be value inreferencing the exponential growth in current as voltage increases past the knee.

I may change my mind as I keep reading throughthis.

[au]Yeah, after reading through everything, if anything, I think that we don't need to discuss this at all.

I'd take the first sentence of that paragraphand replace the first paragraph of the next paragraph.

[av]+joshua@swellfox.

com Josh, if we are notgoing to discuss this anymore, I think it would be better if we will just remove thispart up to the first paragraph of the "What happens inside an LED when it is forward biased?" section.

What do you think? [aw]I think that sounds good! Let's not just delete this, it's good content, honestly, Gary could probably use quite a bit of it for what he's working on.

Let's put it somewhere for reference.

Whether that's at the bottom or in the Trellocard.

[ax]Ohh I see.

So that I won't accidentally delete anything, I'll just place everything at the bottom of this document and just copy the parts thatwe will use in the video and place it at the top.

[ay]Great idea![az]I may have made it worse, not better.

[ba]Starting to wonder if we need this entiresection.

This is more about the operation of an LEDthan how it works.

[bb]+joshua@swellfox.

com Hi Josh! If you think that this part is not neededanymore, yeah, we can just remove this entire section.

[bc]+joshua@swellfox.

com I'll just removeall of these paragraphs.

What do you think? [bd]Perfect![be]Temporary Image.

Stephanie is still working on it.

[bf]Temporary Image.

Stephanie is still working on it.

[bg]E={frac {hc}{lambda }}[bh]I think we could have a stylized version of this pop up on the screen at some point, but reference the fact that we have this on our website as a reference material for furtherperusal.

[bi]Ok Josh! I'll ask Stephanie to make a CB version ofthis table.

[bj]Thank you![bk]I think we could have a stylized version of this pop up on the screen at some point, but reference the fact that we have this on our website as a reference material for furtherperusal.

[bl]Ok Josh! I'll ask Stephanie to make a CB version ofthis table.

[bm]Thank you![bn]I think we could have a stylized version of this pop up on the screen at some point, but reference the fact that we have this on our website as a reference material for furtherperusal.

[bo]Ok Josh! I'll ask Stephanie to make a CB version ofthis table.

[bp]Thank you![bq]I think we could have a stylized version of this pop up on the screen at some point, but reference the fact that we have this on our website as a reference material for furtherperusal.

Ok Josh! I'll ask Stephanie to make a CB version ofthis table.

[bs]Thank you![bt]I think we could have a stylized version of this pop up on the screen at some point, but reference the fact that we have this on our website as a reference material for furtherperusal.

[bu]Ok Josh! I'll ask Stephanie to make a CB version ofthis table.

[bv]Thank you![bw]I think we could have a stylized version of this pop up on the screen at some point, but reference the fact that we have this on our website as a reference material for furtherperusal.

[bx]Ok Josh! I'll ask Stephanie to make a CB version ofthis table.

[by]Thank you![bz]I think we could have a stylized version of this pop up on the screen at some point, but reference the fact that we have this on our website as a reference material for furtherperusal.

[ca]Ok Josh! I'll ask Stephanie to make a CB version ofthis table.

[cb]Thank you![cc]I think we could have a stylized version of this pop up on the screen at some point, but reference the fact that we have this on our website as a reference material for furtherperusal.

[cd]Ok Josh! I'll ask Stephanie to make a CB version ofthis table.

[ce]Thank you![cf]I think we could have a stylized version of this pop up on the screen at some point, but reference the fact that we have this on our website as a reference material for furtherperusal.

[cg]Ok Josh! I'll ask Stephanie to make a CB version ofthis table.

[ch]Thank you![ci]How would you pronounce this word? LEED or LED? I'm assuming LEED but I'm not familiar withthe term "lead frame" and so I could be off base here.

[cj]same as anode lead and cathode lead[ck]So "lead frame" is a thing? I've just never heard of that.

[cl]me neither!but seeing as cathode lead is connected to the lead frame/anvil, I would be super comfortablesaying lead the same way [cm]Hi guys! According to wiki https://en.

wikipedia.

org/wiki/Lead_frameand other sites, "Lead frames are the metal structures inside a chip package that carrysignals from the die to the outside.

" https://image.

slidesharecdn.

com/theledrevolution-141118065629-conversion-gate01/95/the-led-revolution-3-638.

jpg?cb=1416293865 Inside an LED, Anvil and Post are the leadframes or internal metal structures that support the semiconductor material.

[cn]Okay, so it is what I thought it is, it'sjust not a term I've heard before.

I'm going to tell myself that the word "frame"is because it provides some structural stability inside the LED or something.

That'll help me wrap my head around that term.

[co]Sorry, I'm not sure what this means.

I believe that it's just saying that the wireconnects it to the anode terminal but then I could be skipping a step.

[cp]positive lead frame?positive terminal? [cq]Hi guys! According to wiki https://en.

wikipedia.

org/wiki/Lead_frameand other sites, "Lead frames are the metal structures inside a chip package that carrysignals from the die to the outside.

" https://image.

slidesharecdn.

com/theledrevolution-141118065629-conversion-gate01/95/the-led-revolution-3-638.

jpg?cb=1416293865 Inside an LED, Anvil and Post are the leadframes or internal metal structures that support the semiconductor material.

[cr]Temporary Image.

Stephanie is still working on it.

[cs]I'm buying material to make an LED thesize of the mercury vapor bulb we have [ct]That would be an awesome prop and alsoa great office decoration.

.

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