Semiconductors and Their Properties

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Questions and Answers

What is the effect of increasing voltage on the current flow in a forward-biased diode?

The current flow increases sharply after the junction voltage is reached, confirming that the diode is non-ohmic in this range.

What precautions should be taken to ensure safety during the diode experiment?

Precautions include taking multiple readings for accuracy, ensuring clean circuit connections, and using a large series resistor to limit current.

What happens to current flow when a diode is reverse biased?

Only a tiny current flows when the diode is in reverse bias.

How can a pure semiconductor be converted into a p-type semiconductor?

A pure semiconductor can be converted into a p-type semiconductor by adding a small amount of a material like boron that creates holes. Signup and view all the answers

Describe the depletion layer formed at a p-n junction.

A depletion layer at a p-n junction is created when electrons from the n-type region recombine with holes in the p-type region, leaving behind immobile charged ions. Signup and view all the answers

What defines intrinsic conduction in a semiconductor?

Intrinsic conduction is the movement of negative electrons and positive holes in a pure semiconductor. Signup and view all the answers

How does an increase in voltage affect a thermistor's resistance?

Higher voltage causes the thermistor to heat up, which frees more electrons and lowers resistance. Signup and view all the answers

What occurs to the slope of a thermistor's current-voltage graph as the voltage increases?

The slope of the graph becomes steeper, indicating a decrease in resistance. Signup and view all the answers

What happens when the forward voltage exceeds 0.6 V in a diode?

The forward current increases sharply, risking potential damage to the junction. Signup and view all the answers

What role does doping play in semiconductor conductivity?

Doping enhances conductivity by adding another element, creating extra free charge carriers. Signup and view all the answers

What occurs in reverse bias at low reverse voltages?

The reverse current is negligible, allowing the diode to prevent current flow. Signup and view all the answers

In an N-type semiconductor, what are the majority and minority charge carriers?

Electrons are the majority charge carriers, while holes are the minority charge carriers. Signup and view all the answers

What can excessive reverse voltage cause in a diode?

It can lead to junction breakdown and permanent damage to the diode. Signup and view all the answers

How is a P-type semiconductor formed?

By doping a pure semiconductor with a Group III element like boron. Signup and view all the answers

What is the conclusion of the experiment with a p-n junction diode?

Current flows through a forward biased diode, but does not flow through a reverse biased diode. Signup and view all the answers

What is a p–n junction and its significance in semiconductor devices?

A p–n junction is the boundary where p-type and n-type materials meet, forming a diode that allows current to flow in one direction. Signup and view all the answers

What effect does forward bias have on a p–n junction?

Forward bias attracts charge carriers toward the junction, reducing the depletion layer and allowing current to flow. Signup and view all the answers

How does a diode affect alternating current (a.c.)?

It allows current to flow only during the forward-biased portion, converting it to direct current (d.c.). Signup and view all the answers

How is the principle of rectification applied in a mobile phone charger?

The a.c. supply is rectified to produce the required d.c. supply to charge the battery. Signup and view all the answers

What happens to the depletion layer during reverse bias of a p–n junction?

The depletion layer widens, increasing resistance and preventing current flow. Signup and view all the answers

What role does the transformer play in the rectification process?

The transformer adjusts the voltage before it is converted to stable d.c. output. Signup and view all the answers

How does an LED emit light?

When forward biased, light is emitted from the junction, with brightness proportional to the forward current. Signup and view all the answers

What are some advantages of using LEDs?

They offer a long lifespan, low cost, compact size, low operating current, and high switching speed. Signup and view all the answers

What is a transistor used for?

A transistor is used to control the flow of electricity and can function as an amplifier or electronic switch. Signup and view all the answers

What happens to the current in an LDR circuit as light intensity increases?

The current increases with light intensity. Signup and view all the answers

How does the loudness of a buzzer change with the increase in light intensity when connected to an LDR?

The loudness of the buzzer increases as light intensity increases. Signup and view all the answers

What is a thermistor?

A thermistor is a semiconductor device whose resistance changes significantly with temperature. Signup and view all the answers

What are the two main types of thermistors and how do their resistances behave with temperature?

The two main types are NTC (Negative Temperature Coefficient) and PTC (Positive Temperature Coefficient). In NTC thermistors, resistance decreases as temperature increases, while in PTC thermistors, resistance increases with temperature. Signup and view all the answers

What temperature range is tested during the thermistor demonstration experiment?

The temperature range tested is from 0°C in ice water to 100°C in boiling water. Signup and view all the answers

What is the conclusion drawn from the graph in the investigation of thermistor resistance variation with temperature?

The smooth curve indicates that the resistance of the thermistor decreases as temperature increases. Signup and view all the answers

What precautions should be taken during the thermistor investigation experiment?

Ensure sufficient glycerol covers the thermistor, use a digital thermometer for accuracy, and heat the water gradually. Signup and view all the answers

Describe the procedure for observing the variation of current with voltage in a forward-biased semiconductor diode.

Set up the apparatus with a milliammeter in series and a voltmeter parallel to the diode, then increment voltage and record current readings. Signup and view all the answers

What is the primary application of thermistors mentioned in the content?

Thermistors are primarily used for temperature measurement and control. Signup and view all the answers

What happens to the current in the thermistor circuit as the temperature increases?

The current increases as the temperature rises. Signup and view all the answers

What is the defining characteristic of a semiconductor compared to conductors and insulators?

A semiconductor has resistivity between that of a conductor and an insulator. Signup and view all the answers

How does temperature influence the conductivity of silicon?

As temperature increases, more electrons acquire energy to break free from their bonds, enhancing conductivity. Signup and view all the answers

Why does silicon exhibit insulating properties at very low temperatures?

At very low temperatures, all electrons are bound within the covalent bonds, preventing conduction. Signup and view all the answers

What occurs in a pure semiconductor when it is heated?

Some valence electrons gain enough energy to break free from their covalent bonds, becoming conduction electrons. Signup and view all the answers

What is referred to as a 'hole' in semiconductor physics?

A hole is the vacancy left behind when an electron breaks free from its bond, considered positively charged. Signup and view all the answers

Why are free electrons in semiconductors termed 'negative electrons'?

They are called negative electrons because they carry a negative charge. Signup and view all the answers

What characterizes intrinsic conduction in a semiconductor?

Intrinsic conduction involves the movement of charge through a pure semiconductor, with negatively charged electrons moving towards the positive side and holes moving oppositely. Signup and view all the answers

Study Notes

Semiconductors

Semiconductors have outer shell electrons that need a small amount of energy to become free for conduction.
Group IV elements like silicon and germanium have four valence electrons.
A semiconductor has resistivity between a conductor and an insulator.
Pure silicon forms a crystal lattice with covalent bonds between neighboring atoms.
At very low temperatures, silicon acts as an insulator because electrons are bound within the structure.
Higher temperatures provide more electrons with enough energy to break free, reducing resistance and increasing conductivity.

Intrinsic Conduction

Intrinsic conduction is the movement of charge carriers (electrons and holes) in a pure semiconductor.
Negative electrons move towards the positive side, and positive holes move in the opposite direction.
The current in intrinsic conduction is minimal and depends on temperature.

Thermistors

Thermistors are semiconductor devices whose resistance changes significantly with temperature.
NTC thermistors have resistance that decreases as temperature increases.
PTC thermistors have resistance that increases as temperature increases.
Thermistors are used for temperature measurement and control in various applications.

Doping

Doping is adding a small amount of another element to a pure semiconductor to increase its conductivity.
Adding Group V elements (like phosphorus) creates an N-type semiconductor with extra free electrons (majority carriers).
Adding Group III elements (like boron) creates a P-type semiconductor with extra holes (majority carriers).

P-N Junction

A p-n junction is the boundary between p-type and n-type semiconductor materials.
It's crucial for semiconductor device operation.
At the junction, electrons diffuse from the n-type region to the p-type region, and holes diffuse in the opposite direction.
Recombination of electrons and holes creates a depletion layer, a region with fewer charge carriers.
The depletion layer creates a potential difference (junction voltage) – about 0.6V for silicon.

Forward and Reverse Bias

Forward bias: Connecting the positive terminal of a battery to the p-type side and the negative terminal to the n-type side reduces the depletion layer, allowing current to flow easily once the junction voltage is overcome.
Reverse bias: Connecting the negative terminal to the p-type side and the positive terminal to the n-type side widens the depletion layer, increasing resistance and reducing current flow.

Semiconductor Devices

Diodes: Allow current to flow only in one direction.
LEDs: Emitting light when forward biased; the brightness is proportional to the forward current.
Transistors: Semiconductor devices that control the flow of electricity and can act as amplifiers or switches.
LDRs: Light-dependent resistors that change resistance with light intensity; decreasing resistance with increasing light.

Applications and Uses

Rectifiers: Convert alternating current (AC) into direct current (DC).
LEDs: Used as indicator lamps and in display systems (e.g., seven-segment displays).

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Description

This quiz explores the fundamental concepts of semiconductors, including their structure, conduction properties, and the role of temperature in conductivity. Additionally, it covers intrinsic conduction and the function of thermistors. Test your knowledge on these essential components of electronics!