Talk:Semiconductor

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[edit] Unclassified

"What makes semiconductors useful for electronic purposes is that they have the property of being able to carry an electric current by electron propagation or "hole" propagation". Can't this be said with fewer words:

"Semiconductors are useful for electronic purposes because they can carry an electric current by electron propagation or "hole" propagation".

S.

this question about Valence band versus conduction band, and which one is highest or lowest energy? if you add energy, doesn't this excite electrons in the valence band moving them into the conduction band? wouldn't this imply that the conduction band is higher energy? Waveguy

I'm sorry I didn't make this very clear. If you look at the diagram:

Image:Semiconductor band structure (lots of bands).png

The conduction band has a higher energy than the valence band. But the valence band is the highest of the filled bands, and the conduction band is the lowest of the unfilled bands. -- Tim Starling 04:35, Jul 16, 2004 (UTC)

[edit] Not all semiconductors are inorganic

Defining metals and semiconductors by the temperature dependance of their resistances is a gross oversimplification. The reason semiconductors' conductivity increases with temperature is because thermal energy can promote electroncs across the gap, generating the charge carriers that are actually responsible for eletrical conductivity. It is also true that if you shine light on a semiconductor its conductivity will increase because UV/visible light can also promote electrons (especially in organic semiconductors which tend to absorp in the visible region), but you wouldn't define a semiconductor that way. Anyway, the dependance of conductivity on temperature is a function of doping. Overdoping will decrease the conductivity of a semiconductor, for example the conductivity of poly(thiophene) goes through a maximum as a function of dopant right around 1:2 dopant:thiophene unit. Therefore, fully doped poly(thiophene) will become less conductive when heated because the added charge carriers will cause overdoping. It is also worth mentioning that other non-semiconducting systems can show an increase in conductivity as a function of increasing temperature due to ionic conductivity which often becomes accessible to highly charged, non-conjugated (i.e. lacking a band structure) polymers at elevated tempertaures. It is far more accurate to define semiconductors by their band structure because this is in fact the scientific definition of a semiconductor, while the thermal definition is something that physicists often incorrectly mistake for the definition.Fearofcarpet 21:54, 17 Mar 2005 (UTC)


[edit] Semiconductor not defined only by energy bands

I added a few words to the definition. (Are those sentences getting too long?) If we place an electron deep within certain insulators (such as a hunk of resin,) the electron will become trapped in place and will not move significantly when an electric field is applied. On the other hand, if we place the same electron inside a semiconductor, the electron will be freely mobile and will easily flow during an electric field. As insulators, semiconductors behave like vacuums do: they lack trapping centers, and the charges injected by doping, etc., are free to move around. I'm not certain, but I think the definition of "semiconductor" leans more heavily on "lack of trapping centers" than it does on "small band gap." For example, doesn't diamond behave as a very good insulator? Yet diamond also lacks trapping centers, and a diamond-based transistor isn't impossible: see diamond-based semiconductors --Wjbeaty 04:42, Apr 13, 2005 (UTC)

A diamond is simply a "wide bandgap semiconductor". As such it is less conductive than silcion, but still more conductive than an insulator. Its all arbitrary anyway. I believe a semiconductor is rather loosely "defined" as being somewhere between a "conductor" and an "insulator"
By the way, can we have the band diagram on the article page? I shouldn't have to come to the discussion page to find it ;-)
Also, I am thinking of creating a page that deals specifically with the band structure of a semiconductor. What do you all think?--darkside2010 17:46, 15 Apr 2005 (UTC)
"Its all arbitrary anyway." Not at all. While the division between conductor and insulator is certainly arbitrary, "semiconductor" is only arbitrary if we screw up the definition of that word! Is copper a semiconductor? How about polyethelene? If we refuse to draw a line in the sand, then everything is a semiconductor, or nothing is.
Here's another possibility: "a semiconductor is a conductive material whose low electrical resistance is caused by mobile charge carriers contributed by very small amounts of impurities." In other words, if the conductivity is caused by doping, then it's a semiconductor regardless of its band gap width. And notice that this wording excludes materials which are full of trapping centers (if the material is insulating yet is full of *immobile* charge carriers, then it's not a semiconductor.) --Wjbeaty 22:12, Apr 17, 2005 (UTC)
Fair point. An encyclopedia should, after all, define things, and do it well. After reading the opening paragraph of semiconductor again, I think that we could come up with a better definition. So what is it that makes a semiconductor a semiconductor? It has a band gap, sure, but so do all solids - it comes from the quantisation of allowable electron energies around the nucleus. The thing that's different about a semiconductor is that the Fermi level lies somewhere in the bandgap, rather than in an allowable band as it does for a conductor. But then, an insulator also has a mid bandgap Fermi energy, the difference is that the bandgap is so wide that, as it says in the definition, there are not enough electrons in the conduction band at room temperature to allow appreciable current to flow. So, I guess that means that I was half right; the distinction between semiconductor and insulator is somewhat arbitrary. (It comes down to that phrase "appreciable current flow"). But you are right, there is a clear distinction between conductor and semiconductor.
Also I don't think that saying that the mobile charge carriers coming from dopants defines a semiconductor. It does define either an n-type or a p-type semiconductor, depending on the dopant species. But what about intrinsic silicon? Is that not also a semiconductor?
I'm trying to define things dynamically; based on "response to a change" rather than statically; based on "what it is." For a material we can ask what would happen if we take an ultra-pure sample and add tiny amounts of various impurities. If the material is a semiconductor, then certain impurities will create mobile charges. If the material is an insulator, then the impurities will only donate trapped and immobile charges. If the material is a conductor, then large numbers of mobile charges are present even in the pure material. Also, to be "semiconducting" the doping density which produces usable conductivity must be very small. That way the cloud of dopant-produced carriers acts like an easily compressed gas, and the voltages needed to create a depletion zone are easily reached by simple power supplies (try calculating the gate voltage required to sweep all the charges from an FET channel made of copper. Yeesh!) --Wjbeaty 09:31, Apr 19, 2005 (UTC)
As for immobile charge carriers, every solid is made up of (mostly) "immobile" charge carriers. All those protons and electrons that make up the atoms which make up the solid are "charge carriers"; that is, they carry either a positive or negative charge. So I don't think that path helps us to define a semiconductor. The points of distinction from conductors and insulators are mid band-gap Fermi level, and width of the band-gap respectively.darkside2010 12:39, 18 Apr 2005 (UTC)
But in semiconductor physics, the term "charge carriers" always implies current; a "carrier" is a mobile charge, not just a carrier of charge. (Sometimes they call them "current carriers," yet there's no such substance as "current," so the term "charge carrier" would be a bit less misleading to newbies.) Don't lose sight of my original point: as a conductor, silicon is very much like vacuum: if we inject charges into it, those charges will be free to move. But if we inject charges into an insulator (e.g. most plastics,) the charges won't move. I've seen it explained like this: an insulator is full of "trapping centers" caused by lattice defects, and if we inject charges into the material, the charges will bond with the trapping centers and become highly localized.
PS, you'll probably notice that I'm pushing hard for classical-physics models as opposed to QM concepts. Is wikiP a textbook for grad students, or a reference for the general public? Maybe QM is "more accurate," but if our goal is to inform the public, use of QM concepts is similar to use of Latin. At the very least, we need to include concepts graspable by the general public, who are usually regarded as being at the level of intelligent 6th-graders.
Wj, I'm not even sure where to begin. Are you suggesting that we should dumb down the "sum of human knowledge" because it contains concepts which may not be readily understandable to sixth graders? There are some phenomena in this world which cannot be understood without the use of quantum mechanical concepts. The concepts themselves are not difficult to understand. For example, one does not need to be able to solve Schrödinger's equation to be able to understand that electrons in solids are allowed to occupy certain bands of energies and not others. I find your last paragraph particularly strange after reading the rant on distortion of information in physics texts on your homepage.
Sorry, I just don't agree that a semiconductor is like a vacuum. What is the permittivity of a vacuum (free space)? Of silicon? I can't find the values on wikipedia, but I'm hoping that one day I can. The point is that they are not the same. (And what is the analogue of a "hole" in free space?) Even the effective mass of electrons is not the same in a vacuum and a semiconductor.
Earlier you asked what happens if we put an electron deep inside an insulator (resin). How are we going to put the electron there? The point is, we cannot put an electron deep inside an insulator. Why? Because current does not flow in an insulator.
Did you miss my question about intrinsic semiconductors? A semiconductor is not a semiconductor because it has dopants which produce mobile charge carriers (although, this effect is often used, see p-type and n-type). Intrinsic silicon is a semiconductor, even if it is 100% pure. When we introduce dopants, we are actually introducing trapping centres. So your idea to define a semiconductor based on presence or lack of trapping centres is simply wrong (and self-contradictory). Sorry.darkside2010 11:22, 19 Apr 2005 (UTC)

[edit] 1st semiconductor devices and related controversy

The semiconductor devices ruling the market but its first use represents a controversy.The controversy is that one of its 1st use was done by Indian Physicist Sir Jagadish Chandra Bose(30th Nov 1858-23rd Nov 1937) . He ist used the device as a crystal detector in the wave receiver which he created. Moreover he had created a transmitter which could transmit waves as short as 4 mm on the year 1895. He excelled everybody of his time in designing a transmitter and a reciever with a crystal detector. The device was carried to Liverpool and was given a demonstation before The British Association. Due to this contribution he was knighted. His contribution was not given due prominence. until 100 years after his discovery. Discussion initiated by Somnath Majumder

[1] contact me x_planet_ocean_monster@hotmail.com


[edit] Should semiconductor device be merged with semiconductor?

This section inserted as a place to start the discussion about the suggested merge. The first discussion point can replace these two sentences. DFH 17:50, 27 September 2005 (UTC)

This proposed merge is currently under discussion on the WikiProject:Electronics project page. Please place all comments there Thanks--Light current 22:47, 27 September 2005 (UTC)

Thanks to Snafflekid for a thourough kleen up job! I think the two articles can now exist side by side with the disamb notes at the top. Progress should be noted on WikiProject Electronics page.--Light current 16:42, 1 October 2005 (UTC)

[edit] Proposed mergers: Electron-hole pair and Carrier generation and recombination

I proposed two mergers because

  • Both of the proposed merge-ins are mere stubs.
  • Neither contains any information that isn't appropriate here.
  • Neither is being actively edited to increase content.
  • The two proposed merge-ins are redundant -- they overlap each other very heavily.
  • This article would be improved by adding the contents of those two articles.

If there are no objections I will commit the merger within a couple of days. -- The Photon 05:58, 23 January 2006 (UTC)

[edit] Root and branch

The recent edits have made the page fairly unattractive, and the Root page/branch page concept doesn't really fit well here. Should Semiconductor be a branch from Electronics, or from Material science or from Solid-state physics or Metallurgy or Good (economics) or Chemistry or Mineral or ...?

Trying to get everyone to agree to a single classification of everything is the path to madness --- see the justification for the Wikipedia:Categorization scheme.

And breaking up each article into multiple articles for each place it might fit into the root/branch hierarchy is not the answer. What was done to Waveguide just turned one stub article into four useless stub pages, one of which will probably never become a real article (Waveguide (acoustics)), and two of which (Waveguide (electromagnetism) and Waveguide (optics)) overlap immensely since one is just a special case of the other. Trying to do that with Semiconductor would mean breaking the article up into so many pieces that there wouldn't be one place to go if you wanted to actually know what there is to know about semiconductors.

So please use the root and branch scheme where it is appropriate --- but not pages like this that cover a wide territory on their own.

Someone put "Anybody who's reading this is a dork. Anybody who is editing this, have fun. lol loooser". Exact phrasing. -- The Photon 05:49, 28 February 2006 (UTC)

[edit] Mistake

This part shown below is wrong or can be misunderstood. Can somebody correct it, thanks.


"The dopant atom accepts an electron, causing the loss of one bond from the neighboring atom and resulting in the formation of a "hole". Each hole is associated with a nearby negative-charged dopant ion, and the semiconductor remains electrically neutral as a whole. However, once each hole has wandered away into the lattice, one proton in the atom at the hole's location will be "exposed" and no longer cancelled by an electron."

Thoms --130.238.41.162 06:59, 24 May 2006 (UTC)

[edit] Didactic patter

This is supposed to be an encyclopedia article, not notes for a science lesson. There's too much what I call "didactic patter" in some sections of the article. Phrases such is "Note that " and "You would think that ". I just removed one glaringly annoying "It is interesting to note that ", yet the page still needs a further cleanup as regards the use of English. DFH 20:39, 28 August 2006 (UTC)

[edit] Rewrite or delete

This paragraph needs to be rewritten or deleted:

How semiconductors work is a direct result of quantum physics, in particular the Pauli exclusion principle. This principle states that no two fermions can exist in the same state at the same time. Electrons and holes both behave in this way, and the entire electron-hole state is forced to follow certain energy distribution statistics, which basically mean that at any given temperature the distribution of free electrons and holes are statistically determined and predictable. This also means that the conductivity of a semiconductor has a heavy temperature dependency, as a semiconductor operating at very low temperatures (-100°C or so) will have significantly fewer available free electrons and holes able to do the work. If you cool an IC down cold enough, the semiconductor will go intrinsic and all electrical signals will stop. (You would think that heating up the semiconductor has the opposite effect, but there are lots of other problems that happen at high temperatures, including loss of semiconducting properties due to too much free energy, so there is always a happy middle where the semiconductor wants to play!)

DFH 20:46, 28 August 2006 (UTC)

I have just removed the last two sentences from the above paragraph, which had particularly poor style, not up to the quality standard for Wikipedia. DFH 12:19, 29 August 2006 (UTC)

[edit] High and low temperature semiconductors

The article could do with new sections on High temperature semiconductors and Low temperature semiconductors. Some parts of the article are biased towards silicon as the material. DFH 12:04, 29 August 2006 (UTC)

That seems to be more applicable to device operational temperature range than anything else. Semiconductors don't fundamentally change just because of temperature (okay, throwing out VERY high temperatures where it ceases to be a solid). Of course, carrier concentration is very much linked with temperature and the particular material. This should definitely be discussed in this article, but it isn't cause for more article proliferation. There's already enough fragmentation in the semiconductor physics pages. -- uberpenguin @ 2006-08-30 01:14Z

[edit] Mobility

Lacking from the article is any description of the mobility of charge carriers, and the fact that electron mobility and hole mobility are usually different. DFH 12:08, 29 August 2006 (UTC)

[edit] Todo

  • Rewrite the physics section somewhat for clarity and accessibility.
    • Explain the relationship between carrier concentration and temperature a little better
    • explain the term degenerate doping.(done)
  • Finish the carrier concentration section
  • Add lots of decent pictures/illustrations:
    • Better band structure diagram
    • 2D atomic bond model explaining electron/hole carrier concept
    • Nice diagram of typical E-k band structure to illustrate how energy states vary with a particle's wave vector
    • A pretty photo or two... Maybe I'll find them, maybe I'll take them myself...
  • Make the examples less silicon-centric. I'll probably keep using silicon while I'm writing and go back later to mix things up with GaAs and some of the wide- and narrow-bandgap semiconductors.
comment: silicon-centric is the right thing to do. The world of semiconductors is silicon-centric. Probably there should even be a section explaining why. (The Photon)
Let me rephrase, I think it's a good idea to avoid using silicon for every example because it might suggest that silicon is the only important semiconductor. Of course silicon is the most important semiconductor currently because of its advantages for digital VLSI, but that's becoming less and less the case. -- mattb @ 2006-09-11T03:54Z
  • Add a big section on carrier transport mechanics (obviously this will be highly summarized since full articles exist for most of these topics):
  • Somehow, the term lattice constant needs to be linked. There's more to semiconductors than just band structure.(done)
  • History of the development of physical understanding of semiconductors (as opposed to the development of devices).
  • History of the development of semiconductor refining.
  • Economic importance of semiconductors (in raw or refined form, up to the level of unprocessed wafers, but not including ICs or other devices).
  • Any applications of semiconductors outside of electronics? What were they used for before 1947?

Lot of work, anyone looking on, do feel free to chip in and help or at least offer your comments if you think I've missed something. -- uberpenguin @ 2006-08-30 01:04Z

[edit] some major edits to the beginning

Tried to focus the beginning on the commercial/technological importance of semiconductors and on a simple understanding of how they work, to motivate the rest of the article. --Rmalloy 18:35, 2 October 2006 (UTC)

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