Talk:Electron mobility

=Sign issue= Mobility is defined both as v = µE and v = -µE within the article — Preceding unsigned comment added by 2A01:E0A:8F7:4370:3528:469C:E0CC:25E9 (talk) 08:25, 5 July 2022 (UTC)

=Merge Proposal= I propose merging this article with Electrical mobility. I think that article is more fundamental (after all, both electron and ion mobility fall under it), and since they are both stubs (and repeat themselves a lot), there should just be one article. IlyaV


 * I don't think they should be merged. It seems to me that the physics is quite different. The comunities are different, too. I propose to make a reference. (Kehrli (talk) 21:39, 10 June 2009 (UTC))


 * In principle, electron mobility is a special case of electrical mobility. But it's a very important and distinctive special case, enough to warrent its own article. I know this article, right now, is small enough to be part of electrical mobility. But it needs a lot of room to grow, with many topics that are part of electron mobility but not relevant to any other type of electrical mobility--topics like the equations for scattering from phonons, charged defects, uncharged defects, and other electrons, how it affects transistor switching times, and on and on. So I think they shouldn't be merged. But a short summary of this topic should be present in electrical mobility, with a "main article" link. --Steve (talk) 05:18, 11 June 2009 (UTC)


 * More specifically, it seems that electrical mobility mostly describes gases and liquids, so completely different physics. Gah4 (talk) 18:24, 12 April 2018 (UTC)

=Mobility at T=0K =
 * In approximation the mobility can be written as a combination of influences from the lattice and from impurities

If I am not mistaken, in a perfect crystal at absolute zero, mobility is infinite. Therefore it is the impurities and thermal effects that determine mobility, not the lattice at all. CyborgTosser 18:22, 5 Sep 2004 (UTC)

Ok, I retract the previous. When I think about it, it does make sense to identify the thermal effects with the lattice, since a phonon is a lattice vibration. I think it might make sense to change "the lattice" to "lattice vibrations (phonons)". CyborgTosser (Only half the battle) 20:24, 8 May 2005 (UTC)

For the equation
 * $$\mu = \frac{q}{m\nu_m}D$$

what is $$D$$? It certainly isn&#8217;t the $$D$$ that&#8217;s defined below that, since they don&#8217;t even have the same units &#8230; Also, the second equation reduces to
 * $$\mu = \frac{q}{m\nu_m}$$

which implies $$D = 1$$.
 * I think that D was put in by mistake 207.233.110.67 20:53, 9 May 2006 (UTC)

=Lau's hypothesis - Original research?= Looks like the paragraph about Lau's hypothesis was added in March 2007 by 155.69.226.106, somebody from Singapore... The esteemed authors of Lau's hypothesis are also from a Singapore University... I think this hypothesis may be irrelevant to this wikipedia article, smacks of self-promotion by authors. Anybody objecting to deleting it? Xenonice (talk) 01:38, 19 January 2008 (UTC)

=References=

Vague and confusing language
I feel that a statement like "typical drift speed in copper" means nothing. First, it was properly defined that mobility gives (linearized) relation between electric field applied and speed of a charged particle. With this in mind ( and without checking I'll just assume mobility in copper is at least on the order of that of silicon) we get, for a PCB trace of 1mm and voltage difference of 1V => 10V/cm => v ~ 14,000 cm/s, if I'm not mistaken. Much higher than 10^{-4}m/s quoted. Copper will probably melt under these conditions, anyways, but regardless of that, I think that the 'figure' is meaningless.


 * I have recently been editing speed of electricity where the drift speed comes up, and yes it is meaningless. It seems to be computed by dividing by the total electron density, but only conduction electrons contribute. But the actual speed of electrons contributing are at the fermi velocity. I suppose you could divide by the actual conduction electron density. Also, some metals have both electron and hole bands contributing to conduction, such as aluminium, and even more, Al is commonly used for power transmission. I suppose there is that it gives an order of magnitude idea of what happens in a metal, that you can compute without the complications of solid state physics, though. Gah4 (talk) 17:10, 19 March 2018 (UTC)

The highest mobility
I recently read that low temperature mobilities in GaAs of 14 10^6 cm^2/V s have been reported:

Appl. Phys. Lett. 71, 683 (1997); doi:10.1063/1.119829 (3 pages)

I suggest to change the citation. El perseguidor (talk) 18:16, 13 March 2010 (UTC)

Merge with Semiconductor carrier mobility
Two articles on the same topic. OK to merge? --Steve (talk) 21:39, 15 November 2010 (UTC)
 * Personally, I like the distinction between the two articles as they stand. I think there is enough of an audience for people who are interested in just the electron mobility without being interested in semiconductors. I have added an about template that I think summarizes the differences.  Please check and change if necessary.  TStein (talk) 17:54, 16 November 2010 (UTC)
 * This article is almost entirely about semiconductors...with the small remainder being on the more general topic of electrical mobility. If you think, What content would be in a good and thorough discussion of "semiconductor carrier mobility"? The answer is, everything in both of these articles, plus maybe other stuff no one has written yet. Likewise, what content would be in a good and thorough discussion of "electron mobility" that should not be discussed at equal length in an article on "semiconductor carrier mobility"? I can't think of anything, except maybe a few sentences or examples of electron mobilities in metals.
 * Let me be more specific: I propose one article (maybe rename it Mobility (solid-state physics)) including everything in both articles, covering both metals and semiconductors, plus the relevant general aspects of electrical mobility. If you disagree, how would you answer the question: What topics should be discussed in one article but not the other? --Steve (talk) 20:27, 16 November 2010 (UTC)

Since there's not too much objections after 1.5 months, I went ahead and merged to the new article Electron mobility (solid-state physics). :-) --Steve (talk) 17:23, 2 January 2011 (UTC) UPDATE: The newly-merged article was moved back here because it was decided that just "Electron mobility" was a more concise and appropriate title than "Electron mobility (solid-state physics)". (See discussion at Talk:Electron mobility (solid-state physics).) --Steve (talk) 19:59, 14 January 2011 (UTC)

Is the illustration wrong?
Looks like the Hall voltage in "Hall_Effect_Measurement_Setup_for_Electrons" is wrong polarity. Electrons pile up on left side of sample and yet Vh is still shown as positive on the left just the same as the setup for holes illustration! — Preceding unsigned comment added by 71.139.160.159 (talk) 21:17, 18 March 2012 (UTC)


 * I agree, I just switched it. I suspect that the author was trying to indicate how the sign of VH is defined. Either that or a silly mistake. Anyway, you might need to refresh the page to see my new version. --Steve (talk) 22:20, 18 March 2012 (UTC)

I'm wondering about the direction of the electric field along the Y-axis, it seems like the 'Ey' should point toward the direction of the more negative potential, the same as the Hall voltage, so the illustration of the setup for electrons should point to the left, not the right, right?71.139.160.159 (talk) 08:27, 27 March 2012 (UTC)


 * Oh sorry I missed that...fixed! --Steve (talk) 12:08, 27 March 2012 (UTC)

Mobility and Hall Effect Poorly Written
While the equations written down are approximately true for n-type and p-type semiconductors, for any material where both electron and holes are dominant carriers you can't find the hall voltage or mobility of each using the hall effect. The best you can do is for an intrinsic semiconductor where n=p, where you can find the hall mobility times the hall scattering factor, by the usual hall coefficient times conductivity.


 * For an interesting case, aluminium has both electron and hole bands. At high magnetic fields, the hall coefficient goes positive. But otherwise, it has significant electron and hole bands contributing, and so partially cancelling for hall voltage. Gah4 (talk) 16:56, 19 March 2018 (UTC)

metals
The article seems to suggest that holes only count in semiconductors. Many common metals, such as aluminium have significant hole bands, and so should be included in discussion of hole conductivity. In semiconductors, one can usually only consider majority carriers. For metals like aluminium, one needs to consider both at the same time. (Note that aluminium is used for most longer distance power transmission.) Gah4 (talk) 20:33, 16 March 2018 (UTC)


 * That sounds like a reasonable criticism, and I encourage you to try to improve the wording.


 * I might add that the article also neglects the complication that a material can have multiple values of electron mobility (or hole mobility) related to the presence of multiple overlapping bands—or of multiple minima of a single band—e.g. heavy holes vs light holes in GaAs, and the "third band" electrons responsible for the Gunn effect. Or maybe it's OK to leave that out ... a little bit of oversimplification is sometimes OK... :-D --Steve (talk) 01:23, 17 March 2018 (UTC)


 * OK, I removed some restricting words, to allow for holes in metals. Much of the discussion is semiconductor specific. As the article says, mobility isn't especially interesting in metals, as the carrier concentration is high. Gah4 (talk) 02:08, 19 March 2018 (UTC)


 * Thanks! I'd say it doesn't come up as often for metals because the carrier concentration is difficult to appreciably change, as opposed to being high per se. Or maybe I'm splitting hairs. Anyway your changes are good, thanks again. --Steve (talk) 11:55, 19 March 2018 (UTC)


 * That too. Well, one reason that it is difficult to change is that it is high. Big absolute changes are small relative changes. Most people will come here interested in semiconductors, though. Gah4 (talk) 16:52, 19 March 2018 (UTC)

Positive Hall coefficient
I recently added to Talk:Hall effect: It seems that Beryllium, Cadmium, Cerium, Iron, Molybdenum, Tungsten, and a few other metals, have positive Hall coefficients. With one valence electron, it is most likely to have a half full band. (Complicated by crystal symmetry and such, but usually ...) With two valence electrons, it could be a full band (insulator), or two bands more and less than half full. Note also that the metals with positive Hall coefficient also tend to have high resistivity. With one hole and one electron band, the sign will depend on which one is more, and which one is less, than half full, and the mobilities in each. Aluminum has three valance electrons, which can partially fill three bands. So, some hole and some electron bands, and they change with magnetic field. At high magnetic field, Hc of Al goes positive, but is always the result of both holes and electrons. Gah4 (talk) 18:21, 12 April 2018 (UTC)

Regarding why mobility is relatively unimportant in metal physics.
In the fourth paragraph from the top, the author tries to explain why the electron mobility is an unimportant factor to examine for metal conductivity.

To quote "Conductivity is proportional to the product of mobility and carrier concentration. For example, the same conductivity could come from a small number of electrons with high mobility for each, or a large number of electrons with small mobility for each. For metals, it would not typically matter which of these is the case, since most metal electrical behavior depends on conductivity alone. Therefore mobility is relatively unimportant in metal physics".

Now, because most metals have high mobility, therefore, conductivity depends on carrier concentration alone and that's why mobility is not so important. Therefore, the word "conductivity" (see above in quoted paragraph in bold ) in bold should be replaced with "carrier concentration" in the second last line of the paragraph. Otherwise, with the current version, it seems like the author is saying that the conductivity of the metals depends on the "conductivity" alone, which doesn't mean anything.

Please let me know if I am mistaken in my thought process.

Thanks — Preceding unsigned comment added by 74.70.220.40 (talk) 23:03, 16 November 2019 (UTC)


 * Hmmm. In semiconductors, carrier concentration is relatively low, and its value is often important. The turn-off time for a bipolar transistor, maybe for an FET, too, depends on how fast you can get carriers out, which depends on mobility, since it is concentration that you are trying to get low. In metals, carrier concentration is pretty much constant, and doesn't depend, for example, on current. If carrier concentration is constant, then it is mobility that determines conductivity, which is much higher than in semiconductors. Gah4 (talk) 01:56, 17 November 2019 (UTC)

can only happen in ternary or higher alloys
The article says that alloy scattering can only happen in ternary or higher alloys. Seems to me that it should also happen in SiGe alloys, which are binary alloys. Otherwise, yes, for III-V compound semiconductors is is ternary and higher. Gah4 (talk) 08:27, 16 December 2019 (UTC)

Einstein relation (classical case not relevant for metals)
Previously classical version of the Einstein relation was used. For most metals, one needs a quantum version with temperature replaced by the Fermi energy. I did a minimal change, but the text should better be improved. Daniel Antonenko (talk) 18:30, 4 July 2023 (UTC)