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.

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 a page with information and links.

“BCE” refers to “Base Collector Emitter,” which are the names of the three leads on a bipolar transistor.

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.

You also need inductors (solenoids).


I also forgot about resistors.

More specifically, *bipolar junction transistors contain two PN junctions. Field-effect transistors are another matter.

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.

Desmostylus: cite please?



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:

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.