Given that we just finished learning about this concept in our last chapter (yay!), I figured I'd talk about some of the things that we learned. Below is a picture of a computer switch, an essential computer component that only requires the simple action of turning it ON or OFF, but involves really complicated physics behind it (it took me a long to understand how it worked...).
A computer ON / OFF switch is the application of transitors, specifically MOSFET (Metal-Oxide-Semiconductor-Field-Effect-Transistor), which is a 3-terminal semiconductor device that can work either as strong resistors or strong conductors. A MOSFET transistor is a lightly doped p-type semiconductor whith two islands of n-type material placed avoce a substrate (one is source S, one is drain D). An n-channel connects the S and D while an insulator covers the substrate and the two islands and metal gate G is placed above the transistor.
When the gate voltage = 0 (potential difference between source S and drain D), electrons flow from the negative terminal to the source S, then across the n channel to drain D and eventually to the positive terminal. Therefore, a current flows through the transistor when the gate voltage is 0. This is how the transistor funcitons when the the copmuter is switched ON.
On the other hand, when there is a negative gate voltage, the gate is negatively charged. The electrons are driven out of the n channel and the n channel is therefore depleted fo electrons (less n electrons). The electrons repel each other and the electric field they cause drives the n channel's electrons into the p-doped substrate to occupy holes. As the n channel becomes narrower and with a strong electric field in the gate, no electrons can flow from source S to drain D. Therefore, current cannot flow. This is what happens when the computer is switched OFF.
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