Okay, welcome to the course understanding diodes and transistors. And right now we're going to talk about semiconductor basics. And what's a semiconductor? Well we know that conductors are mediums in which their current flow in electronic circuit in other words, if I have a conductor I can have electron flow very nicely, okay we have examples of conductors, copper, silver, gold, aluminum. And if, if you remember from my previous courses, okay, we talked about balance electrons, and conductors have valence electrons. And if you remember, valance electrons are very easily dislodged or freed from orbit.

So if I put an electrical pressure on their voltage, it's very easy for me to get these free electrons to flow through the conductor. Alright, which happens to be again copper, silver gold aluminum, and and for the most part any type of metals. Alright, so we have conductors and then we have semiconductors. So let's go on to the next slide. Alright, so if we look here we see semiconductors do not allow electrons to flow as easily as conductors. That's why they're called semiconductor.

All right, conducts a little bit and, of all the materials sillicon is the most common All right, you'll you'll hear I'm sure you heard the term silicon on a chip or anything okay those are silicon we have silicon diodes silicon transistors, silicon II seeds which is integrated circuits okay these this is a doping procedure for so we can make these integrated circuits that that promote some type of electronic circuit action. Okay. But more importantly here is if you looked at a conductor, which we saw on the previous slide, okay semiconductors have four valence electrons on their outer shell. All right, we're conductors only had one. And since there was only only one valence electron in a conductor atom IE gold, silver and so forth, it was very, very easy to dislodge that electron from its outermost orbit around the atom around the nucleus of the atom.

So right here, okay, we have four valence electrons. And it's a little bit more difficult. That's why it's called a semiconductor. All right. One of the ways in a semiconductor that we can increase the amount of electron flow is by heating, heating the element heating the chip, right? That's why if you look on some of the integrated circuit specifications, they'll say they'll give you a temperature range and they don't want to go above some temperature range and I think military is is is a lot tighter than commercial.

But I and I want to say I want to say 50 degrees C. on military, I could be wrong, but I want to say that and if we if we go above that temperature, then what we'll do is we'll have a greater current flow and the properties of the the either the transistor, the diode or the integrated circuit won't, it won't adhere to the actual design of that. Okay, we get something called thermal runaway, which, which we probably don't want to do in, in, in a design in electronic design. So, that's what we mean by a semiconductor. Okay, again, my semiconductor has four valence electrons around the nucleus of the atom, and it's in the outermost orbit. Okay, let's look at this one here. So basically, we have a semiconductor with four valence electrons.

Okay. And when we combine them in in some silicon atom, you'll notice that we're sharing each center of the atom is sharing two electrons in there. So is my silicon atom. And when I put them side by side or use a process of putting them into the bonded silicon, okay, we have two electrons in the outermost shell, where each one or each nucleolus is sharing those valence electrons. All right. So let's play the slide off and go to the next one.

All right, if we add an impurity to this substrate or this, the silicon wafer, okay. In this case we're adding an n type semiconductor material. It's actually called arsenic. We're adding an arsenic atom there. Okay? Look at what happens.

All right, we're adding an and actually we're adding one additional electron in the outermost shell and look at what happens. All right, we have one atom here. And I'm sorry one electron there. And that electron is shared by this atom, this silicon atom and this silicon atom. So if you look, wouldn't that electron be easily dislodged from orbit and we can do this same thing. If we Use an electron.

That's minus I'm sorry, an atom that's minus an electron. In this case, we have a boron atom. And what happens is, we have a missing electron, which is called a hole. So now we have an extra hole. All right? So wouldn't it be easy to move this hole from atom to atom in this silicon wafer?

Okay, now basically what we're showing here is how either electrons or holes flow with with our different semiconductor materials. So we've got in type, we've got p type semiconductors. Obviously, if you've taken previous courses from me, what happens is, electrons will flow this way. And so because of the chemical reaction of the battery. And we know from previous discussions, we've got an excess of electrons. What happens is the battery pushes electrons through the n type semiconductor to the positive terminal of the battery, which has a shortage of electrons.

And that action continues until the chemical action of the battery decays, okay? Same thing here. With p type material. Instead of using electrons, we're using whole flow. Remember, we hit that's a shortage of electrons and they flow. I'm sorry, hole flow goes this way.

All right, flows against the battery. Okay. In other words, this is mine. So my holes flow this way but We still have a electron flow. Okay, cousin aunt because in a semiconductor we have majority carriers and minority carriers and majority carriers and electrons and minority carriers are the holes or the plus signs. So that's really all I want to get into here.

I mean, well then we're really going to get into physics and I just, I mean, that's not what this is about. This is a practical electronic course. Okay? So just look at that. I'm going to clear the slide. We're going to go to the next one.

Okay, now let's see what happens when we put up and type silicon material and p type silicon material. All together. And what happens is, as we're showing right here, these electrons want to do what they want to equalize. So we set up a depletion area right there, where it's neutralized. In other words, the the, the p type material has a shortage of electrons and the n type material has a surplus of electrons. So what happens is, we create what they call a depletion area where everything is neutralized.

Okay? And since it's neutralized, it kind of acts as an insulator. Alright, so now what happens is we put a battery on and we fall with bias, this silicon and what happens is, we have current flow Excuse me, we have electron flow this way. All right. All right, those are the majority carriers. We also have a little bit of whole flow in the opposite direction.

If you're looking here what we showing that and that is they call that the minority, the minority carriers All right. This is also you'll hurt hear the term leakage current All right. So there could be some leakage current going. In other words, when I when I put a voltage across here, I have conduction as we show you here this way, right? All right. That's I want all my current to flow that way.

But because of the impurities and because of semiconductor is not 100% we have What they call minority carriers, which are leakage currents, which actually flow in the opposite direction. Okay, obviously, what do I want? I want my majority carriers to be the majority of current fall like then they call majority carriers. And I want them in already carriers to be ideally, we don't want any of them. But if we have to have some of them, we want them to be very, very, very, very small. All right, and you may hear the term leakage currents.

Well, the minority carriers are the leakage current. All right, and each silicon or each semiconductor has its own characteristics on that. Right. We can find the current flow through and this would be the majority right here. Okay, a battery is six volts and we have a voltage drop across our silicon a 610. And it's just ohms law.

I go through, I do my mathematics and I find out that the current flow when I have 1000 ohm resistor there with a 606 volt voltage source, then I have a count of 5.4 milliamp hours. That's it. Now, this will end this little subject of of semi what I call semiconductor basics. Yeah, we've got a little bit more in this course. We're going to talk about diodes and circuits and transistors. But this is just to give you an idea.

As a practical engineer, you really, for the most part, you really don't have to know how this works. It's just an overview. Okay, as a practical engineer, we need to know about current flow and voltage And impedances or resistance that we're driving, and we'll get into that. I mean, that's really all I want to say here. Okay, as we progress through this, you'll see what I mean. All right.

So I'm going to clear the slide off. And we're going to go on to the next section now. See over there. Take care.