Understanding Diodes: Internal Composition and How They Work in a Circuit

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Transcript

00:00In this video, we'll explain what diodes are, their internal composition, and how they function in a circuit.

00:07A diode is essentially an electronic check valve for current.

00:10It allows current to flow in one direction, but blocks it in the opposite direction.

00:15Diodes typically have a marking on one end, which indicates the cathode, while the unmarked end is the anode.

00:22When the cathode is connected to the negative terminal of a power supply,

00:26and the anode is connected to the positive terminal,

00:29the diode behaves like a closed switch, allowing current to pass through.

00:33However, when the polarity is reversed, the diode acts as an open switch and blocks the flow of current.

00:40This unique property is due to the semiconductor materials that make up a diode.

00:44The most common semiconductor used is silicon.

00:47Let's consider a silicon atom, which has four valence electrons in its outermost orbit.

00:52These valence electrons bond with neighboring silicon atoms through covalent bonding

00:57to form the crystalline structure of silicon.

01:00In its pure state, there are no free electrons available to conduct electricity,

01:05so silicon behaves like an insulator.

01:08However, when external energy in the form of voltage is applied,

01:12some electrons break free from the covalent bonds,

01:15becoming free electrons that can move through the crystal and conduct electricity.

01:20This transformation makes silicon a semiconductor, transitioning from an insulator to a conductor.

01:26Pure silicon, however, is not sufficiently conductive for use in diodes.

01:30To enhance its conductivity, a process called doping is employed.

01:35Doping involves introducing atoms of another element into the silicon crystal.

01:39For example, when a phosphorus atom, which has five valence electrons, replaces a silicon atom,

01:46four of its valence electrons bond with neighboring silicon atoms,

01:50while the fifth electron remains free to move through the crystal, enabling electrical conduction.

01:55Since electrons are the mobile charges in this scenario, this process is known as n-type doping.

02:02On the other hand, p-type doping involves introducing a boron atom, which has only three valence electrons.

02:08A boron atom needs an extra electron to complete its bonds with neighboring silicon atoms,

02:14leaving behind a vacancy called a hole, which behaves like a positively charged particle.

02:19As the hole moves by, attracting electrons from neighboring atoms,

02:23it creates new holes, which is referred to as hole movement.

02:27Since holes are the mobile charges in p-type doping, it is called p-type doping.

02:32In a diode, one side of the semiconductor is doped as p-type, and the other side is doped as n-type.

02:40These are known as the p-region and n-region of the diode.

02:44At the junction between these two regions, electrons from the n-region and holes from the p-region

02:49are attracted to each other, trying to cross the junction.

02:53Once a sufficient number of charges cross, they create a depletion region that prevents further charge flow.

02:59When the p-region is connected to a positive potential, and the n-region to a negative potential,

03:04the electrons and holes are pushed toward the center of the diode.

03:08However, the depletion region blocks them from moving further.

03:12The electrons and holes in the depletion region are held together by a certain force.

03:17Once a voltage greater than 0.7 volts is applied, these forces are overcome,

03:22and the charges are free to move.

03:25This allows current to flow through the diode.

03:27This process is called forward biasing.

03:30In contrast, when the p-region is connected to a negative potential, and the n-region to a positive potential,

03:37the electrons and holes are attracted towards the terminals and accumulate there.

03:41This widens the depletion region, blocking the flow of current through the diode.

03:45This condition is known as reverse biasing.

03:48And that's how a diode works.

03:50I hope you learned something from this video.

03:52Don't forget to subscribe and turn on notifications to see future uploads.

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