# Diodes **URL:** \ **Category:** Factual Questions\ **Created:** [March 10, 2003, 11:33pm UTC](https://boards.straightdope.com/t/diodes/160437 "2003-03-10T23:33:26Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![SlickRoenick](https://avatars.discourse-cdn.com/v4/letter/s/e68b1a/32.png) [@SlickRoenick](https://boards.straightdope.com/u/SlickRoenick)\ **Post date:** [March 10, 2003, 11:33pm UTC](https://boards.straightdope.com/t/diodes/160437/1 "2003-03-10T23:33:26Z")
Are diodes and transistors the same thing? Does it have something to do with the BCE (CBE?) line up? Or am I totally lost. I guess I need a good electronics link. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [March 10, 2003, 11:42pm UTC](https://boards.straightdope.com/t/diodes/160437/2 "2003-03-10T23:42:34Z")
A diode is a single PN junction, and has two leads. A transistor is two PN junctions arranged either PNP or NPN, and has three leads. [Here’s](http://www.solarbotics.net/bftgu/starting_elect_semic.html) a page with information and links. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [March 11, 2003, 12:27am UTC](https://boards.straightdope.com/t/diodes/160437/3 "2003-03-11T00:27:09Z")
> [@](#): > > \*Originally posted by Muldoon III \* > **Does it have something to do with the BCE (CBE?) line up?** “BCE” refers to “Base Collector Emitter,” which are the names of the three leads on a bipolar transistor. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [March 11, 2003, 7:17am UTC](https://boards.straightdope.com/t/diodes/160437/4 "2003-03-11T07:17:26Z")
If you take silicon and add certain types of impurities you basically make what they call N and P type silicon. Silicon is grown as a crystal, so if you grow a layer of N type silicon then grow a layer of P type silicon you end up with a diode. A diode is a device that conducts electricity in one direction but not in the other, sort of a one way valve for electricity. A one way valve is very useful. Consider an AC electrical source. If you put a diode in the circuit, then it will pass all of the positive swings of the AC wave and block all the negative swings. Now you have only positive swings, and if you put something like a capacitor on there, the time it takes to charge and discharge the capacitor will smooth out the variations in the posive swings, and you’ve essentially converted AC to DC. The same basic procedure (rectification and filtering) converts AM radio signals to voice. If you make three layers, you make what is called a bipolar junction transistor (BJT). Basically you have two choices, you can start with N first or you can start with P first, so the silicon layers will go either NPN or PNP. The middle is called the base (because the first one they made was sitting on this part). The outside parts are called the collector and emitter. The interesting thing about this device is that if you have it set up a certain way, you can control how much current flows from the collector to emitter by varying the current that goes into the base. If you use the current to turn the current flow completely on and off you are basically using it as an electrically controlled switch. If you don’t turn it all the way on or off, then a small variation in the base current makes a larger variation in the current flowing from the collector to emitter. In other words you just made an amplifier. Typically, digital circuits will drive transistors all the way between cutoff and saturation (completely off and on) and analog circuits keep them somewhere in the middle (called the forward active region of the transistor). With diodes, transistors, and capacitors (which are just two metal plates), you can make just about anything. Google “electronics tutorials” for more detailed info. ---
**Author:** ![Urban\_Ranger](https://avatars.discourse-cdn.com/v4/letter/u/e9c0ed/32.png) [@Urban\_Ranger](https://boards.straightdope.com/u/Urban_Ranger)\ **Post date:** [March 11, 2003, 7:22am UTC](https://boards.straightdope.com/t/diodes/160437/5 "2003-03-11T07:22:13Z")
You also need inductors (solenoids). ---
**Author:** ![Urban\_Ranger](https://avatars.discourse-cdn.com/v4/letter/u/e9c0ed/32.png) [@Urban\_Ranger](https://boards.straightdope.com/u/Urban_Ranger)\ **Post date:** [March 11, 2003, 7:23am UTC](https://boards.straightdope.com/t/diodes/160437/6 "2003-03-11T07:23:25Z")
:smack: I also forgot about resistors. ---
**Author:** ![JThunder](https://avatars.discourse-cdn.com/v4/letter/j/e95f7d/32.png) [@JThunder](https://boards.straightdope.com/u/JThunder)\ **Post date:** [March 11, 2003, 7:27am UTC](https://boards.straightdope.com/t/diodes/160437/7 "2003-03-11T07:27:57Z")
> [@](#): > > \*Originally posted by Q.E.D. \* > \*\*A diode is a single PN junction, and has two leads. A transistor is two PN junctions arranged either PNP or NPN, and has three leads. [Here’s](http://www.solarbotics.net/bftgu/starting_elect_semic.html) a page with information and links. \*\* More specifically, \*_bipolar junction transistors_ contain two PN junctions. Field-effect transistors are another matter. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [March 11, 2003, 7:35am UTC](https://boards.straightdope.com/t/diodes/160437/8 "2003-03-11T07:35:43Z")
> [@](#): > > \*Originally posted by engineer\_comp\_geek \* > **If you take silicon and add certain types of impurities you basically make what they call N and P type silicon. Silicon is grown as a crystal, so if you grow a layer of N type silicon then grow a layer of P type silicon you end up with a diode.** It isn’t done that way. The silicon is grown as a mostly pure crystal ingot, which is then further purified by varous means, and sliced up into thin wafers. These wafers then have layers of P- or N-type dopants infused into them in specially-designed ovens, using carefully-controlled processes, and are then cut apart to separate the individual components. ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [March 11, 2003, 8:00am UTC](https://boards.straightdope.com/t/diodes/160437/9 "2003-03-11T08:00:55Z")
> [@](#): > > \*Originally posted by Q.E.D. \* > \*\*It isn’t done that way. The silicon is grown as a mostly pure crystal ingot, which is then further purified by varous means, and sliced up into thin wafers. These wafers then have layers of P- or N-type dopants infused into them in specially-designed ovens, using carefully-controlled processes, and are then cut apart to separate the individual components. \*\* It often _is_ done that way. The wafer that you start with is the substrate. The other stuff is grown on top by epitaxy. ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [March 11, 2003, 6:36pm UTC](https://boards.straightdope.com/t/diodes/160437/10 "2003-03-11T18:36:50Z")
**Desmostylus** : cite please? ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [March 11, 2003, 11:20pm UTC](https://boards.straightdope.com/t/diodes/160437/11 "2003-03-11T23:20:02Z")
[http://www.informatik.uni-stuttgart.de/ipvr/ise/Skripte/Prof\_B\_Skripte/MSS\_Skript/MSS\_3c.pdf](http://www.informatik.uni-stuttgart.de/ipvr/ise/Skripte/Prof_B_Skripte/MSS_Skript/MSS_3c.pdf) [http://www.eecs.umich.edu/~singh/bk7ch08.pdf](http://www.eecs.umich.edu/~singh/bk7ch08.pdf) ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [March 11, 2003, 11:36pm UTC](https://boards.straightdope.com/t/diodes/160437/12 "2003-03-11T23:36:25Z")
[Epitaxy.](http://www.reactiontechnology.com/serv1.htm) The epitaxial layers are vapor deposited on the silicon substrate, not grown at the time the substrate is, as the poster, **engineer\_comp\_geek** I was responding to had stated: > [@](#): > > Silicon epitaxy (epi) is usually deposited onto silicon wafers used to manufacture semiconductors devices, such as discrete transistors or integrated circuits. Epi is the chemical vapor deposition of crystalline silicon of a specified thickness, impurity type, and resistivity tailored to meet the exact specifications of the consumer. > > Depending on the device type, the epitaxial layer is deposited either on raw substrates or substrates with previous processing (buried layers). ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [March 12, 2003, 12:45am UTC](https://boards.straightdope.com/t/diodes/160437/13 "2003-03-12T00:45:32Z")
Well, don’t take it too literally. I was just trying to explain the basic process to someone with little knowldge of semiconductors. I didn’t mean to imply that they stopped the silicon pull and changed the doping right then and there. When you condense a complicated process down to about half a sentence some of the details do get a little fuzzy.