Talk:Photodiode

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Hi there. Can someone please put some stuff up for the construcion and how th photo diodes work please?

What are some possible reasons photodiodes do not reach saturation?


I think that this article needs to mention semiconductor physics or link to a discussion therein. Therobotbuilder 19:57, 12 November 2006 (UTC)


I have some conservation of energy angst. The diode's built-in field is what accelerates the electrons to create the drift velocity (hence current) in the diode. So the energy that is generated from a photovoltaic cell would seem to come from the p-n junction (and its' charge carrier gradient), not the light source which generated the electron-hole pair in the first place. I know the light must be the source of energy behind the current that is generated, but I can't quite see how. can anyone explain? Andybuckle 16:48, 15 January 2007 (UTC)


"electrons that are generated by photons in the base-collector junction _are injected into the base_" in the description of phototransistor work in the first para. Is that true? Aren't the electrons swept into the collector, increasing its current and the holes gather in the base region increasing its voltage? --Janislaw 10:35, 16 January 2007 (UTC)


Picture

Can Someone confirm that the pictures is actually a photodiode. It looks like an LED. 194.200.145.5 13:24, 2 February 2007 (UTC)

An LED can serve as a photodiode. In fact, every diode is photosensitive. --Phil Roan, 71.116.81.130 (talk) 00:15, 24 December 2007 (UTC)

Reverse Bias[edit]

The article states that reverse-biasing "strengthens the photocurrent". Does this refer to some minor effect, or is it just false? If you're getting only one electron per photon, the current will be set by the photon rate and be independent of applied voltage. Also, I'm not familiar with the effects of "expanding the reaction volume". Is that going to create better efficiency? I thought the only reason to reverse-bias a photodiode was to reduce the capacitance, thereby increasing the response speed. Spiel496 15:54, 24 May 2007 (UTC)

Spiel is correct. Reverse bias does not strengthen the photocurrent (For a visual see the graph at [1]). In fact, the article has it backwards. Reverse bias causes photocurrent, decreasing the sensitivity of the device. However, it significantly lowers the capacitance, which causes improvements in the response time because the time constant is a product of the load resistance with the junction capacitance. --Phil Roan, 71.116.81.130 (talk) 00:15, 24 December 2007 (UTC)


Picture of square device looks exactly like a solar battery I have from an LCD power supply. Much different in that it creates electron flow versus controls electron flow. Now about that gain in a phototransistor.

Graphs or schematics[edit]

It might help to add a graph with I-V curves under different levels of illumination or a schematic for an equivalent circuit, e.g. current source (dependent on light level) in parallel with a regular diode and possibly some resistors or capacitors Nrnkpeukdzr (talk) 04:20, 13 January 2008 (UTC)

A graph similar to Figure 1 in the Encyclopedia of Laser Physics article on Photodiodes would be helpful. http://www.rp-photonics.com/photodiodes.html — Preceding unsigned comment added by 129.215.139.65 (talk) 18:29, 21 June 2011 (UTC)

Photocurrent polarity[edit]

The photocurrent flows from cathode to anode, against the diode's arrow. This can be confirmed by the graphs at [2]: the photocurrent is negative but the current from "turning the diode on" is positive. The polarity paragraph is wrong, the first paragraph of Principle of Operation is correct. 128.146.36.20 (talk) 02:21, 2 October 2008 (UTC)

I think it used to say that photo-electrons flowed with the diode's arrow -- that would have been correct. It looks right now, though. Spiel496 (talk) 17:29, 2 October 2008 (UTC)

Phototransistor: Faster or slower?[edit]

Under "Other_modes_of_operation" it says "Phototransistors also have slower response times." but the article on "Photoresistor" says "Phototransistors react much quicker to light change. As such, they're preferred for receiving data." and links to this section. Which is it? —Preceding unsigned comment added by 72.37.171.52 (talk) 14:16, 21 November 2008 (UTC)

A Photodiode is faster than a Phototransistor, at least if it is the sensor that sets the speed. The Phototranistor is often faster than a typical Photoresitor. However there are also some special very fast Photoresistors, even comparable to fast photodiodes. --Ulrich67 (talk) 22:18, 12 January 2011 (UTC)

Incorrect redirection[edit]

Obviously photo transistor have nothing to do with photo diodes, yet somebody seemed to have mislinked the two together.

(To the post above) As for their speed, a photo diode should be faster than a photo transistor, which in turn is faster than a photo resistor. Both the photo diode and the photo transistor can be used for receiving data. Interarticle (talk) 12:58, 19 September 2009 (UTC)

photo diode[edit]

please explain how the photo diode works —Preceding unsigned comment added by 117.254.157.237 (talk) 12:20, 30 September 2009 (UTC)

"at least one of these sentences is wrong"[edit]

Someone put a superscript saying that at least one of these is wrong, but made no mention of what was wrong on this talk page (that I can find):

1. Due to the intrinsic layer, a PIN photodiode must be reverse biased (Vr). The Vr increases the depletion region allowing a larger volume for electron-hole pair production, and reduces the capacitance thereby increasing the bandwidth.
2. The Vr also introduces noise current, which reduces the S/N ratio. Therefore, a reverse bias is recommended for higher bandwidth applications and/or applications where a wide dynamic range is required.
3. A PN photodiode is more suitable for lower light applications because it allows for unbiased operation. (*at least one of these sentences is wrong!)

I suspect that they have misread number three to be referring to the PIN photodiode rather than a PN. I can't think of a way to rewrite the sentence to rely less on the PN vs PIN wording, but the content (when properly read) seems sound to me.

Because I can't see a problem with any of the sentences, I have removed the superscript.

118.208.163.172 (talk) 07:01, 30 April 2010 (UTC)

There is a slight Problem with Sentence no 1. It's not really wrong, but misleading. It's true that the depletion region gets larger in a PIN diode, but the increase in sensitivity is way smaller than the increase in volume. In a PN-diode most electron hole pairs created close the junction also contribute to the current. The sensitive range is about one diffusion length (e.g. 200 µm) beyond the junction. It's only close to the long wavelength limit (e.g. more than about 950 nm in silicon) that the electron - hole pairs are created deep inside the material so that the sensitivity goes down. Here a PIN diode can have a slight advantage. --Ulrich67 (talk) 22:48, 12 January 2011 (UTC)

The "at least one" was a bit of an understatement, since all three are deeply flawed. In 2, the Vr does not introduce noise current unless the junction is leaky. In 3, I have no idea what's behind it. Dicklyon (talk) 02:49, 13 January 2011 (UTC)
That section came from this hit-and-run editor: Special:Contributions/24.20.100.227. I think I'll just take it out. Dicklyon (talk) 04:06, 13 January 2011 (UTC)

Comparison with photomultipliers[edit]

Somebody flagged this comparison section as needing references and threatens to remove the section. I strongly urge that it be kept. It is very difficult to provide references on twenty different statements or more. Readers can certainly check the validity of any of the statements if needed. I really like sections like this in Wikipedia articles and would urge critics to lighten up a little on them. The authors who post them should be commended for clarifying the differences between similar topics that may otherwise be confusing to people. I say keep it. 3dimen (talk) 13:53, 7 August 2011 (UTC)

photovoltaic mode- vs photodiode mode[edit]

Apparently in both vases the cathode shld be positive. That is wrong as these are different modes. In Voltaic mode it should be in conductivity mode with the cathode on the minuw — Preceding unsigned comment added by 88.159.150.221 (talk) 16:01, 29 September 2011 (UTC)