Semiconductors have revolutionized our lives. But have you ever pondered how?
Every day, our lives resemble scenes from science fiction movies. We can now communicate, shop, bank, and scan information without leaving our homes using our phones or computers. It is fair to state that semiconductors are among the reasons why science and technology are changing our lifestyle.
Imageuse of semiconductors
So, what does semiconductors work? What unique features do semiconductors offer that will revolutionize our lives?
Electrons conduct electricity in materials. Materials are classified as conductors, insulators, or semiconductors based on their electrical characteristics. This classification is based on the density of freely flowing electrons in the substance, not the total quantity of electrons. Because while all materials include electrons, the density of free-floating electrons influences conductivity. The density of free electrons in a substance determines its "excellent conductor" status.
Copper, gold, and silver are good conductors of electricity due to their high free electron density. Free electron density is low in insulators like plastic, porcelain, wood, and paper. So they don't conduct electricity.
What are Semiconductor materials?
They are materials whose conductivity varies between conductor and insulator. While doping semiconductors can modify the density of free electrons, it cannot change the density of free electrons in conductors or insulators. In other words, unlike insulators and conductors, semiconductors' conductivity can be altered. The energy band structure of semiconductors allows this.
In general, solid energy bands resemble atomic energy levels. While atoms form solid substance, their energy levels form energy bands. Just as in atoms, electrons in solids can only be found in certain energy ranges (such as conduction band and valence band). The forbidden band is named thus because it lacks electrons. To further comprehend semiconductor energy bands, we need to know how semiconductors differ from metals. The “conductivity type” is this.
Conduction band electrons migrate in metals. There are two bands in semiconductors. These are the conduction and valence bands. Adding doping atoms to semiconductors increases their conductivity while also determining the electron transmission band. Semiconductors that transport electrons from the valence band are called “n-type.”
Image conductor vs semi conductors transmission bands
So what if semiconductors have two distinct conduction bands? The relevance of semiconductors is highlighted by "semiconductor junctions" generated by adding semiconductors.
Why?
A “semiconductor junction” is generated by joining an n-type and p-type semiconductor. This joint only carries current in one direction. That is, electrical conduction becomes asymmetric! Metals lack this characteristic. A metal wire, like copper wire, conducts electricity symmetrically in both directions.
Electrical qualities originate from the symmetry of semiconductor junctions. Because these structures can be combined to form three-terminal circuit elements.
Electronic circuit parts like resistors, coils, and capacitors have two terminals. They conduct current depending on the voltage between their terminals. The voltage differential between these two ends controls the wire's current. Simple functions like decreasing voltage and changing alternating current to direct current can be achieved with these circuit parts.
Three-terminal circuit elements, however, are unique. The third end can control the current between the two ends. A transistor has three prongs.
Image2- and 3-terminal circuit elements
Initially, this property of three-terminal circuit elements may appear trivial. But this isn't the case. By combining logic gates and powerful processors that can process information, decision-making electrical circuits and computers can be constructed.
In reality, three-terminal circuit elements are at the heart of the technology that altered our lives. Was this related to semiconductors? Do transistors need semiconductors to function?
first eniac
ImageFirst electronic computer ENIAC
Sure, it's doable. Vacuum tubes were utilized as transistors before semiconductors. But vacuum tube transistors have significant drawbacks. First, they were massive. So much so that the early vacuum tube computers were almost as big as houses and weighed tons. The ENIAC, the first computer using vacuum tube transistors, was 167 square meters and 30 tons. Also, the vacuum tubes started working after a few minutes. Vacuum tubes have to be heated to work properly. Vacuum tubes could not be made smaller to fit in today's integrated circuits.
Vacuum tubes
Imagevacuum tubes
Due of their electrical properties, semiconductor materials were employed to build transistors in the 1940s. So billions of transistors in tiny integrated circuits could be produced. Our lifestyle has changed thanks to three-terminal circuit parts, notably transistors, made from semiconductors.
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