By Robert Hazen, Ph.D., George Mason University
Let’s focus on how semiconductors devices work. A single piece of n- or of p-type semiconductor material in itself is just a lousy conductor of electricity. However, the magic begins when you put two or more of these pieces of semiconductor materials together and join them physically into a single device. The simplest semiconductor device is called a diode.
How Does a Diode Work?
A diode is simply a piece of n-type material attached to a piece of p-type material with two wires. Diodes are extremely common in modern electronics. They’re very small. They’re made of a tiny piece of silicon with an n-type at one end, a p-type at the other end, and two wires coming out of the ends. Think about what happens in a situation where you have this sort of arrangement of semiconductor materials.
If electric current flows into the negative side of a diode, it wants to flow right on through to the positive side because negative electrons are attracted to the positive end. In fact, the resistance is almost zero in this direction. But, if you have electrons flowing into the positive end, they stop dead because negative electrons don’t want to go toward the negative side of the diode, and the resistance in that direction is almost infinite.
What you have, then, is a one-way valve for electricity. And there’s no simple combination of conductors and insulators that can accomplish that.
This is a transcript from the video series The Joy of Science. Watch it now, on Wondrium.
Plugging in an Electronic Device
When you plug an electronic appliance into the wall, the first device that the electricity sees is going to be a diode, and that’s because most electronic devices can’t use the alternating current that comes out of your wall, electronic devices need direct current. If you ever dismantle an old TV or a radio, what you are likely going to find is that the electricity enters in—the power comes in with the two wires—and the first object it hits inside that device is a diode.
This is true of almost all electronic devices. If you can imagine what this looks like, you can think of the current entering into the diode as having a kind of a wave-like character, going back and forth, sloshing back and forth. When it comes out of the diode at the other end, you just have a series of pulses of electrons going in the same direction.
Capacitors and Transistors
Those pulses aren’t a very good way to control electricity in a device, you need yet another semiconductor device, this is called a capacitor or a condenser. A capacitor, or condenser, acts for all the world like a miniature rechargeable battery that recharges very quickly. You pump electrons into this device; it charges up, and out the other end flows a direct current. Therefore, if you have most electronic devices these days, after the current comes in and sees the diode, the next thing it sees is a capacitor, and the capacitor changes AC into DC current. That’s just the beginning of what semiconductor devices can do.
The next step is to make a three-layer sandwich, and a three-layer sandwich of semiconductor material is called a transistor. Transistors can be n-p-n, or they can be p-n-p. The transistor was invented at the AT&T Bell Laboratories in New Jersey shortly after World War II as part of what was then a great boom in industry-sponsored basic research. The three Bell Labs scientists, John Bardeen, Walter Brittain, and William Shockley shared the 1956 Nobel Prize in Physics for this great invention. By the 1970s, transistors had virtually replaced the vacuum tube in all routine applications.
Learn more about electromagnetism.
Advantages of Transistors
The transistor has many advantages. One of them is its extremely small size. Some of them are microscopic, they’re only about the size of the head of a pin. Even the large power transistors are quite small. These transistors replaced vacuum tubes, often called triodes, and the vacuum tubes were much larger, they used a thousand times more power, generated lots of heat, were likely to burn out, and were expensive.
This is a revolution in electronics that really changed the way you could use electricity and changed the kinds of appliances that everybody could have in their homes. Transistors now find all sorts of use in modern electronics, especially as amplifiers and as logic circuits. The principal use of transistors is as an amplifier. It takes a weak variation in power or in voltage coming in and amplifies it so that the output is a very strong variation in power or voltage.
Learn more about how materials are useful because of a variety of optical, thermal, magnetic, and electrical properties.
Microchip: The Amazing Semiconductor Device
The heart of many modern appliances is the microchip. The microchip is an integrated circuit: this is a single semiconductor device that may incorporate thousands and thousands of transistor-like regions. Microchips are tiny. It’s amazing how many different n- and p-type regions can be contained in one of these small devices. These microchips are deposited layer by layer in vacuum chambers.
As successive layers form, different masks control the amount of n- and p-type regions that are deposited. Microchips are used to control the application of almost all modern electronic devices, and you may have seen some of the old, wonderful circuit boards that contain tens or hundreds of these microchips.
Common Questions about How Semiconductor Devices Work in All Modern Electronic Appliances
Diodes are a form of semiconductor device found in most electronic devices. This tiny semiconductor device is made of silicon and consists of an n-type semiconductor at one end as well as a p-type semiconductor at the other end.
Since diodes can’t control electricity well, another semiconductor device called a capacitor is required. The capacitor acts as a rechargeable miniature battery, commonly used with diodes in most electronic devices.
Microchips are found in many home appliances today. Microchips are very small semiconductor devices made up of thousands of transistor-like regions. The device is an integrated circuit.
