What Are the Main Differences Between Semiconductors and Insulators?
Based on whether it is electricity or heat that passes through a material it is called electrical conductivity or thermal conductivity respectively. So, it is a measure of the tendency of a material to allow current or heat to flow through it. The resistivity decreases as the conductivity increases. In metals, it is assumed that all the outer electrons are free and available to carry a charge and the only impedance is if they bump into each other.
Semiconductors:
The two types of junctions mentioned earlier are the p-type and n-type junctions. The "p" type is the positive side and "n" type is the negative side. The positive side has an excess of holes and the negative side has an excess of electrons. The p-n junction is created by the process of doping. There are different processes, like implantation, diffusion of dopants and by growing a layer of crystal doped with one type of over a layer of crystal that is doped with another type. The last process is called epitaxy. The p-n junctions are considered to be the basic building blocks of semiconductors. These are used in LEDs, transistor circuits, diodes etc: A p-doped semiconductor is a better conductor. Even a n-doped one is a good conductor. The junction between them, however, is comparatively non-conductive and depends on the relative voltages of the two semiconductor regions. When you apply a voltage across a p-n junction it is called a BIAS. When the current flow is easy it is called forward bias and when current flow is less or difficult it is called reverse bias. At the junction region, the free electrons of the n-type are attracted to the positive holes in the p-type. They diffuse, canceling each other out. This results in an uncharged and electrically neutral region.
In a Forward bias, the p-type is connected to the positive terminal and the n-type is connected to the negative terminal. When connected in this way, the positive holes and the negative electrons are pushed towards the junction. The positive charge repels the holes and the negative charge repels the electrons. Although the electrons penetrate only for a very short distance into the p-type material, current flow will continue without interruptions.
Connecting the P-type to the negative terminal and N-type to the positive terminal causes a reverse bias. Very little current will flow and the diode will break down.
Insulators:
Uses of Insulators:
As mentioned before, a flexible coating of insulating material is applied on electric wires. This is called insulated wire. When conducting wires touch each other, it can create a short circuit and damage to appliance hence insulation of the wires is important. Also, wires that expose voltages higher than 60v can cause shock to human beings and hence should be insulated. In electronic systems, the printed circuit boards are made from epoxy materials which are good insulators.
In high voltage overhead transmission wires, they are bare and not protected with any plastic coating but they are insulated by air. Insulation supports are used while fixing long distance transmission of high tension wires. Insulation materials for such high voltage lines are made of ceramic, glass or porcelain. Dirt, pollution, salt or water on the insulator can cause a conductive route and this cause leakage currents and flashovers. There are different types of insulators like pin type, post insulator, strain insulator etc: For high voltage transmissions, the suspension insulator strings are used.
The first electrical systems that used insulation were the telegraph lines. It is because when the wires were directly attached to the wooden poles during damp weather it gave bad results in terms of performance. First glass was used as an insulator and then ceramic was introduced in the industry by manufacturers in London.
The most important insulation material that is naturally available is air. A multitude of solid, liquid and gaseous materials are also used. Sometimes polymer varnish films are used in motor coils. Earlier asbestos was also used as an insulator but then given the carcinogenic nature of asbestos it is now banned.
Finally, there are two classes of insulation. They are class 1insulation and class 2 insulation.
Class 1 insulation mandates that the metal body and other exposed metal parts should be connected to the earth via a grounding wire.
Class 2 insulation means double insulation. It is used in some appliances like shavers, dryers etc: all energized internal components are enclosed inside an insulating body and should not come in contact with live parts.
FAQs on Semiconductors and Insulators Explained
1. What are conductors, insulators, and semiconductors? Provide an example for each.
Conductors, insulators, and semiconductors are materials classified based on their ability to conduct electricity.
- Conductors are materials that allow electric current to flow through them easily because they have many free electrons. Example: Copper, Aluminium, Silver.
- Insulators are materials that strongly resist the flow of electric current. They have virtually no free electrons. Example: Wood, Glass, Rubber.
- Semiconductors are materials with electrical conductivity between that of a conductor and an insulator. Their conductivity can be controlled by adding impurities or changing the temperature. Example: Silicon (Si), Germanium (Ge).
2. How does the energy band theory explain the key difference between semiconductors and insulators?
The energy band theory explains this difference based on the forbidden energy gap (Eg), which is the energy difference between the valence band and the conduction band.
- In insulators, this energy gap is very large (Eg > 3 eV). It requires a huge amount of energy for an electron to jump from the valence band to the conduction band, so they do not conduct electricity under normal conditions.
- In semiconductors, the energy gap is relatively small (Eg < 3 eV). At room temperature, thermal energy is sufficient for some electrons to jump this gap, allowing for a limited flow of current.
3. What is the difference between an intrinsic and an extrinsic semiconductor?
The main difference lies in their purity and conductivity.
- An intrinsic semiconductor is a semiconductor in its purest form, without any added impurity atoms. Its conductivity is low and depends primarily on temperature. Example: Pure Silicon.
- An extrinsic semiconductor is an intrinsic semiconductor to which a specific impurity has been intentionally added. This process, known as doping, is done to significantly increase its conductivity and control its electrical properties.
4. Explain the formation of N-type and P-type semiconductors.
N-type and P-type semiconductors are two types of extrinsic semiconductors formed by doping.
- N-type Semiconductor: Formed when a pure semiconductor (like Silicon) is doped with a pentavalent impurity (an element with 5 valence electrons, e.g., Phosphorus). Four electrons form bonds, and the fifth becomes a free electron, increasing conductivity. In N-type, electrons are the majority charge carriers.
- P-type Semiconductor: Formed when a pure semiconductor is doped with a trivalent impurity (an element with 3 valence electrons, e.g., Boron). The three electrons form bonds, creating a vacancy or a "hole" where an electron is missing. This hole acts as a positive charge carrier. In P-type, holes are the majority charge carriers.
5. Why does a semiconductor’s conductivity increase with a rise in temperature?
A semiconductor's conductivity increases with temperature because the charge carriers are created by thermal energy. As temperature rises, more valence electrons gain enough energy to break their covalent bonds and jump into the conduction band. This process creates more free electrons and holes (electron-hole pairs), which are the charge carriers. An increase in the number of charge carriers directly leads to higher conductivity and lower resistivity. This is in sharp contrast to metals, where rising temperature increases atomic vibrations, hindering electron flow and increasing resistance.
6. What is a p-n junction, and how is its depletion region formed?
A p-n junction is the interface or boundary formed between a P-type and an N-type semiconductor. This junction is the fundamental building block of diodes and transistors.
The depletion region is formed instantly when the junction is created. Due to the concentration difference, electrons from the N-side diffuse to the P-side, and holes from the P-side diffuse to the N-side. This diffusion causes electrons and holes to recombine near the junction. As a result, a region is created near the junction that is depleted of free charge carriers. This region contains only immobile positive and negative ions, creating a potential barrier that opposes further diffusion.
7. What happens when a p-n junction diode is in forward bias versus reverse bias?
The behaviour of a p-n junction diode changes drastically depending on the applied voltage polarity.
- Forward Bias: The P-type region is connected to the positive terminal of a battery and the N-type region to the negative terminal. This applied voltage opposes the potential barrier, reducing the width of the depletion region. It allows majority charge carriers to cross the junction easily, resulting in a high current flow.
- Reverse Bias: The P-type region is connected to the negative terminal and the N-type to the positive terminal. This applied voltage supports the potential barrier, increasing the width of the depletion region. It blocks the flow of majority charge carriers, resulting in a very low (almost zero) current flow.
8. Explain the main application of a semiconductor diode as a rectifier.
The primary application of a semiconductor diode is as a rectifier, which is a device that converts alternating current (AC) into direct current (DC). This is possible because of the diode's unique property of allowing current to flow in only one direction (when in forward bias) and blocking it in the other (when in reverse bias). When an AC voltage is applied across a diode, it conducts only during the positive half-cycles (forward biased) and does not conduct during the negative half-cycles (reverse biased). This effectively cuts off half of the AC wave, resulting in a pulsating DC output.
9. How do special-purpose diodes like LEDs and photodiodes work in everyday devices?
LEDs and photodiodes are examples of p-n junction diodes designed for specific interactions with light.
- LED (Light Emitting Diode): An LED is a heavily doped p-n junction that, when forward biased, emits light. The energy released when electrons and holes recombine at the junction is converted into photons of a specific colour. They are used in lighting, displays, and indicators due to their high efficiency and long life.
- Photodiode: A photodiode is operated in reverse bias and is designed to detect light. When light with sufficient energy strikes the depletion region, it creates electron-hole pairs. The reverse bias voltage sweeps these carriers across the junction, producing a small current that is proportional to the light intensity. They are used in light detectors, smoke alarms, and optical communication systems.
