What is a semiconductor?

Question

clear explanation of semiconductors

Answer 1

Its half way between an electrical conductor and an electrical insulator. Its resistance increases with temperature

Answer 2

semiconductors have resistance midway between conductors and insulators.

but, wat makes them so much useful in the electronic industry is their atomic structure. p-type and n-type semiconductors, when used in close adjacency(as a junction) becomes a device, diode whose resistance can be varied by varying the bias(voltage applied) across it. such two junctions used back-to-back forms a transistor. A transistor can function as a switch. all our ic's, processors are stuffed with millions of such transistors.

their resistance being midway between conductors and insulators just happens by chance and is another characteristic feature of theirs.

Answer 3

Ok, first, you have to understand what  elements are made of. According to bohr's model, an atom, which is the smalest amount of an element that keeps it's properties, is made of a certain number of protons, neutrons and electrons. Think of it as the solar system, where the sun will be the protons and the neutrons and the planets will be  the electrons.

Well, there are levels where the electrons can be, like the orbits of the planets. The level we care about right now is the outern level, where the furthest and last electrons of the element are. This is the valence layer and these electrons are callede the valence electrons. You can see the number of them in the periodic table.

In ideal conditions, the electrons will stay in this valence layer, but when you apply heat or light or whatever source of energy to the element, these electrons pass to another layer called the conduction layer.

When the electrons leave the valence layer, they leave a hole there and that's when you get what it's called a positive ion. And the electron is free to travel to another atom and this is what makes current possible.

In good conductors, due to the metalic bonding, the valence layer and the conduction layer cross each other, permiting the electrons to flow freely. It's like a sea of electrons ready to flow.

Now, semiconductors are made of Silicium or germanium. The Si and the Ge have four valence electrons which are the electrons in the outern layer of them.

Let's use the Si from now on. When you have a crystal of Si, you have what it's called a covalent bond. This means that two atoms that are placed together share twoo electrons with each other, causing the Si atom to get 8 valence electrons. The problem is that in this structure you can't have a nice flow of electrons due to their stability. All the flow you get will come from the electrons that got out of place because of heat flow or light flow or whatever. This electron hole creation is called a pair.

Now, we have a flux in this material, but we need a bigger flow or electricity, so what do we do? we dope them. That's what you call when you introduce impurities to the cristal in order to get more electrons in the conduction layer without creating holes or when you introduce impurities to the cristal in order to get more holes without getting electrons in the conduction layer.

When you want to get a lot of electrons in the conduction layer, you dope the Si or Ge with atoms with 5 valence electrons, called pentavalent atoms. This is because when they join the Si atoms, there will be a free valence electron that will pass to the conduction layer. This is called an N type semiconductor.

The same happens when you want to add holes to the material, but instead of adding a 5 valence electron atom to the structure, you add a 3 valence electron atom to the structure getting a free space or a hole, this is called a P type semiconductor. N for negative and P for possitive. This is because it is said taht an electron carries a negative charge and a hole a positive one. This is because the scientist made this convention a long time ago.

Well, the thing is that these properties of the material give you a conductivity between 0 for isolators and infinitum for ideal conductors. And this is the basis for all semiconducting devises there are out there.

You may wonder, why use Si instead of Ge. The reason is that Si has more resistance than Ge due to the size or their atoms.

Hope this helps.