Photodiodes - (working & why it's reverse biased) | Semiconductors | Physics | Khan Academy

Let's explore the working of a photodiode - a PN junction that converts light into electricity - its working, its applications, and why it's reverse biased.
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Created by Mahesh Shenoy

[@AJ-td1sb]

I'm currently doing an electrical engineering course. I mute the lecturer to listen to your explanation instead. Terrible isn't it. But thanks very much for putting these up.

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The content is amazing and your accent makes it 10 times better! This is the very first time I am finding physics interesting! Thanks

[@Ivan0001]

*electronics

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@@Ivan0001 its a part of a chapter in physics genius!

[@divyamkumarpandey7749]

Please add this video to the semiconductors playlist

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You made incredible sense than my lecturer and he has one more than an hour video on this and still doesn't make any sense.

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[@techrajix]

It was a great explanation sir

[@spurti]

Ohh the electrons from the negative terminal (electron flow) fills out the holes in p type material. Conversely the electrons from the n type side is reaching towards the positive terminal of the battery so the depletion layer is increased and if we finished this process then the current would not flow in a reverse bias mode.

[@atomicreactions9201]

Exactly. I am learning this topic a the moment, and he confused me lot, that he is doing it the other way arount.

[@atomicreactions9201]

Oh never mind. I was wrong my self. Because of the charge double layer, which results out of the will of the to potentials to get equivalent, the electrons forming on the p-side are directe moving to the n-side because the first space on the n-side is positivly charged. The result in the end is a potenzial difference and a resulting current.

[@spurti]

@@atomicreactions9201 are you talking about reverse or forward bias mode?? Like I would recommend you to watch a video on diodes by ochem tutor on youtube. So that you get the basic concept and come back here and watch solar cells,photodiode and led.

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[@anamikapratiyush7364]

Excellent explanation, however the bossing in forward condition is not correct

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विवरण और ग्राफिक्स, दोनों ही बहुत अच्छे हैं। Hats off to you dude and to Khan academy!!!

[@anitathomas5506]

thanks sir

[@sm-pz8er]

Thanks for the video. Why the current is from right to left not left to right? toward N junction?

[@qzorn4440]

is the current flow direction due to the electron movement or the void of an electron hole movement as an electron in a vacuum???

[@beartheburn3863]

Shouldn't be the positive ion of the depletion region be containing the holes ?? 5: 22

[@karlberggren2042]

Nice video. My only suggestion is that the i v curve should not go to the origin. Even at v=0 you should see significant photo current, I believe.

[@lewtube6436]

I agree -- because the depletion region is still present at v = 0 (albeit a non-expanded one), and it's in this region the current is generated.

[@user-ez9ex8hx6v]

Yess

[@SD-mc9xm]

The electron absorbing the energy from the photon sounds like the photoelectric effect

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Hmm

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[@Chillandrelax2475]

Hi, how to calculate a resistor value for a photodiode?

[@lumiluppy8294]

Hi! What do you mean add a diffuser in photodiode?

[@jigyasaagarwal6161]

Can you tell me the reason of negative current ??

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Best content in this term

[@niranjan7457]

Sir at 07:43 You mentioned that we want the current only due to light so we don't use forward biasing (as another current flows) But in reverse biasing, a current flows (not due to photons) but it's very small. So we are neglecting that current, right?

[@radhakrishnajha5084]

Ofcourse

[@avijitmudgal7554]

Off course...see the current generated in the depletion layer is enormously small as compared to the current which is generated by light.

[@debarshidas8596]

No, I think it is included in dark current

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[@aramugamselvavadivel5262]

what software are you using to explain

[@samikshachauhan6078]

Is this same happen in pin photodiode

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best

[@akhilseelam3741]

00:02 Photodiodes convert light to electricity and are used in detecting brightness 01:39 Reverse biasing in photodiodes limits current and widens depletion region. 03:08 Light absorption in semiconductors creates electron-hole pairs 04:32 Light absorption generates current in semiconductors 06:01 Photodiodes detect brightness using reverse bias. 07:27 Photodiodes work in reverse bias to ensure current is only due to light. 08:54 Current generated by photodiodes is independent of voltage after a certain point due to the number of electron-hole pairs formed by the light. 10:15 Photodiodes can generate a tiny current even in absence of light due to thermal energy.

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Suppose if the light brightness is maximum, then will the current flow or the depletion region will blast...???

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[@redhoodiestudio]

It makes no sense to me that the free electron would recombine outside of the depletion region, because we apply an electric field with our reverse bias. Or what do I see wrong?

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[@petermarsh4993]

Dear Sir, I have a problem which you may be able to help me solve. I have a new Solar Panel installation and I want to use it in part to heat my underfloor heating through the electrical conduction wires embedded in my concrete floor. The problem is, when sunlight dims during the day, electricity comes from the grid to maintain a consistent flow of electricity to heat my floor. Grid electricity is expensive and I NEVER want to use grid electricity to heat the floor, only solar derived electricity. I was thinking of combining two devices to make a switch that turned on the output to the floor from my solar panels when the sun is shining and turn off current when the sun is not shining. The thought was to use a Photodiode as the current switch that is connected via a low voltage power supply to a solenoid. This solenoid switches off 240V power to my underfloor heating when the solar radiation {and therefore current in the low voltage circuit} drops to below a certain level and stops power going to the heater circuit. If the sun reappears from behind a cloud, the circuit goes back on again. What do you think about my problem and do you have any suggestions? Thanks.

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can this be used in automatic doors which open when we go near it??????

[@tasneem6427]

We are not light emitting bodies. So I don’t think so 👀

[@deepanshu564]

infra-radiation detection is used in heat cameras for automatic doors

[@Pushed2InsanityYT]

Possibly if you have some bright light shining at the sensor and you happen to block that light when you come near the door, current will decrease, and door can open, but I think this can raise many false alarms. Like what if a fly just cover up the sensor, or something.

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Correct the accent! The KHurrent dosent sound so good to listen to.

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Sir, what are used in Solar panels, photodiode or solar cells???

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Solar cells

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Sir if you will teach this in hindi then your growth will become 10x

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[@bdas2267]

Your accent is quite irritating. Please try to speak in Indian accent instead of copying other countries accent. Otherwise videos is good.

[@raphaelcardoso7927]

Very good explanation