Electricity is essentially the movement of free electrons between atoms. Copper is a popular choice for wiring because it has a lot of free electrons, making it an excellent conductor of electricity. To keep us safe, we use rubber to insulate these copper wires, as rubber is an insulator. This means its electrons are tightly bound and cannot move freely between atoms.
In a metal conductor, an atom consists of a nucleus at the center, surrounded by orbital shells that hold electrons. Each shell can hold a specific number of electrons, and electrons need a certain amount of energy to occupy these shells. The electrons farthest from the nucleus have the most energy and are located in the outermost shell, known as the valence shell. Conductors typically have one to three electrons in this valence shell. These electrons are held by the nucleus, but there’s another shell called the conduction band. If an electron reaches this band, it can escape the atom and move freely.
In metals like copper, the conduction band and the valence shell overlap, allowing electrons to move easily. In insulators, the outermost shell is full, leaving little room for electrons to move. The nucleus holds these electrons tightly, and the conduction band is far away, preventing electron movement and thus, electricity flow.
Semiconductors, such as silicon, have properties between conductors and insulators. Silicon’s outermost shell has too many electrons to be a conductor, so it behaves like an insulator. However, the conduction band is close enough that with some external energy, electrons can jump from the valence band to the conduction band, allowing them to move freely. This dual behavior makes semiconductors unique.
Pure silicon has almost no free electrons, so engineers modify it by adding small amounts of other materials, a process known as doping. This creates p-type and n-type silicon, which are combined to form a diode. A diode has two leads: the anode and the cathode, connected to thin plates. Between these plates, there’s a layer of p-type silicon on the anode side and n-type silicon on the cathode side, all encased in resin for protection.
In pure silicon, each atom is surrounded by four other silicon atoms, sharing electrons to fill their valence shells, a process called covalent bonding. When we add n-type material like phosphorus, it replaces some silicon atoms. Phosphorus has five valence electrons, so when silicon atoms share electrons, there’s an extra electron left over, free to move. For p-type doping, materials like aluminum are used, which have only three valence electrons. This creates a “hole” where an electron can sit.
When these doped materials are combined, they form a PN junction. At this junction, a depletion region is created where excess electrons from the n-type side fill holes on the p-type side. This movement forms a barrier with electrons and holes on opposite sides, creating an electric field that prevents further electron movement. The potential difference across this region is typically about 0.7 volts in standard diodes.
When a voltage source is connected across the diode, with the anode (p-type) connected to the positive and the cathode (n-type) to the negative, it creates a forward bias, allowing current to flow. The voltage must exceed the 0.7-volt barrier for electrons to move across.
If the power supply is reversed, connecting the positive to the n-type cathode and the negative to the p-type anode, the barrier expands, and the diode acts as an insulator, preventing current flow.
That’s the essence of how diodes work! For more learning, explore additional resources and videos, and stay connected with us on social media and our website, engineeringmindset.com.
Engage with an online simulation that demonstrates how electrons move in conductors, insulators, and semiconductors. Observe the behavior of electrons in different materials and adjust parameters to see how doping affects electron flow. This will help you visualize the concepts discussed in the article.
Using a breadboard, diodes, and basic electronic components, construct a simple circuit to observe diode behavior. Test the circuit with different voltage sources to see how diodes allow or block current flow. This hands-on activity will reinforce your understanding of diode functionality.
Participate in a group discussion to explore real-world applications of semiconductors and diodes. Research and present on topics such as solar cells, LED technology, or microprocessors. This will deepen your understanding of the importance of semiconductors in modern technology.
Analyze a case study on doping techniques used in semiconductor manufacturing. Discuss the impact of different doping materials and methods on the electrical properties of semiconductors. This activity will enhance your knowledge of how doping modifies semiconductor behavior.
Take a quiz designed to test your knowledge of diode characteristics, including forward and reverse bias, the PN junction, and the role of the depletion region. This will help you assess your understanding and identify areas for further study.
Here’s a sanitized version of the provided YouTube transcript:
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As you may know, electricity is the flow of free electrons between atoms. We use copper wires because copper has a lot of free electrons, which makes it very easy to pass electricity through. We use rubber to insulate the copper wires and keep us safe because rubber is an insulator, which means its electrons are held very tightly and cannot move between other atoms.
If we look at the basic model of an atom for a metal conductor, we have the nucleus at the center, surrounded by a number of orbital shells that hold the electrons. Each shell holds a maximum number of electrons, and an electron must have a certain amount of energy to be accepted into each shell. The electrons located farthest from the nucleus hold the most energy. The outermost shell is known as the valence shell, and a conductor has between one and three electrons in this valence shell. The electrons are held in place by the nucleus, but there’s another shell known as the conduction band. If an electron can reach this band, it can break free from the atom and move to another.
With a metal atom such as copper, the conduction band and the valence shell overlap, making it very easy for the electron to move. In contrast, with an insulator, the outermost shell is packed, leaving very little room for an electron to join. The nucleus has a strong grip on the electrons, and the conduction band is far away, so the electrons cannot reach it to escape. Therefore, electricity cannot flow through this material.
However, there’s another material known as a semiconductor. Silicon is an example of a semiconductor. With this material, there are too many electrons in the outermost shell for it to be a conductor, so it acts as an insulator. But since the conduction band is quite close, if we provide some external energy, some electrons will gain enough energy to jump from the valence band into the conduction band and become free. Therefore, this material can act as both an insulator and a conductor.
Pure silicon has almost no free electrons, so engineers dope the silicon with a small amount of another material to change its electrical properties. We call this p-type and n-type doping. We combine these two materials to form a diode. Inside the diode, we have two leads: the anode and the cathode, which connect to some thin plates. Between these plates, there is a layer of p-type doped silicon on the anode side and a layer of n-type doped silicon on the cathode side. The whole assembly is enclosed in resin to insulate and protect the materials.
Let’s imagine the material hasn’t been doped yet, so it’s just pure silicon. Each silicon atom is surrounded by four other silicon atoms. Each atom wants eight electrons in its valence shell, but the silicon atoms only have four electrons in their valence shell. So, they share an electron with their neighboring atom to achieve the desired eight. This is known as covalent bonding.
When we add n-type material such as phosphorus, it takes the position of some silicon atoms. The phosphorus atom has five electrons in its valence shell, so as the silicon atoms share electrons to get their desired eight, they don’t need this extra one. This results in extra electrons in the material, which are free to move. With p-type doping, we add a material such as aluminum. This atom has only three electrons in its valence shell, so it cannot provide its four neighbors with an electron to share. As a result, one of them will have to go without, creating a hole where an electron can sit.
Now we have two doped pieces of silicon: one with too many electrons and one with not enough. The two materials join to form a PN junction. At this junction, we have what’s known as a depletion region. In this region, some of the excess electrons from the n-type side will move over to occupy the holes in the p-type side. This migration forms a barrier with a buildup of electrons and holes on opposite sides. The electrons are negatively charged, and the holes are considered positively charged. This buildup causes a slightly negatively charged region and a slightly positively charged region, creating an electric field that prevents more electrons from moving across. The potential difference across this region is about 0.7 volts in typical diodes.
When we connect a voltage source across the diode, with the anode (p-type) connected to the positive and the cathode (n-type) connected to the negative, this creates a forward bias and allows the current to flow. The voltage source must be greater than the 0.7-volt barrier; otherwise, the electrons cannot make the jump.
When we reverse the power supply, connecting the positive to the n-type cathode and the negative to the p-type anode, the holes are pulled towards the negative, and the electrons are pulled towards the positive. This causes the barrier to expand, and therefore, the diode acts as an insulator to prevent the flow of current.
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This version maintains the technical content while ensuring clarity and readability.
Electricity – A form of energy resulting from the existence of charged particles such as electrons or protons, typically manifesting as an electric current. – The principles of electricity are fundamental to understanding how circuits function in electronic devices.
Electrons – Subatomic particles with a negative charge, which orbit the nucleus of an atom and are involved in forming electric currents. – In a conductor, electrons move freely, allowing electricity to flow through the material.
Conductors – Materials that allow the flow of electrical current with minimal resistance due to the presence of free electrons. – Copper is widely used in electrical wiring because it is an excellent conductor.
Insulators – Materials that resist the flow of electric current, often used to protect or separate conductors. – Rubber is commonly used as an insulator to coat electrical wires and prevent accidental shocks.
Semiconductors – Materials with electrical conductivity between that of a conductor and an insulator, often used in electronic components. – Silicon is the most commonly used semiconductor material in the production of integrated circuits.
Doping – The intentional introduction of impurities into a semiconductor to change its electrical properties. – By doping silicon with phosphorus, engineers can create n-type semiconductors with enhanced conductivity.
Junction – A region where two different types of semiconductor materials meet, crucial in the operation of devices like diodes and transistors. – The p-n junction is a fundamental building block in semiconductor technology, allowing for the control of current flow.
Current – The flow of electric charge carried by electrons through a conductor, typically measured in amperes. – The current flowing through the circuit was measured to ensure the device operated within safe limits.
Voltage – The electrical potential difference between two points in a circuit, which drives the flow of current. – Increasing the voltage across a resistor will increase the current, according to Ohm’s Law.
Silicon – A chemical element with semiconductor properties, widely used in the manufacture of electronic components and solar cells. – Silicon wafers are the foundation of modern microelectronics, serving as the substrate for integrated circuits.
