Semiconductor Junctions: Diffusion Current

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Questions and Answers

What is the color of the positively charged side of the junction's depletion region?

Blue

Green

Red (correct)

Yellow

What type of bias is represented in the region where the current is nearly zero?

Forward bias

Total bias

Zero bias

Reverse bias (correct)

Which diagram correctly represents reverse bias?

Neutral bias diagram

Zero bias diagram

Reverse bias diagram (correct)

Forward bias diagram

What does the term 'bias' mean in the context of a PN junction?

The direction of the external voltage Signup and view all the answers

What is the result of forward biasing a PN junction?

The current through the junction increases Signup and view all the answers

What is the depletion region of a PN junction?

The region around the junction where the charge carriers are depleted Signup and view all the answers

What happens to the depletion region during forward bias?

It narrows Signup and view all the answers

What is the energy required for electrons to pass through the depletion region equal to?

Barrier potential Signup and view all the answers

What is the result of the energy loss when electrons cross the depletion region?

A voltage drop across the pn junction Signup and view all the answers

What is the effect of the internal resistance of the material on the voltage drop?

It has a negligible effect on the voltage drop Signup and view all the answers

What is the purpose of reverse biasing a diode?

To prevent current through the diode Signup and view all the answers

What happens to the depletion region during reverse bias?

It widens Signup and view all the answers

What happens to the majority carriers in the n region during reverse bias?

They are depleted Signup and view all the answers

What happens in the p region during reverse bias?

Electrons enter as valence electrons and move toward the depletion region Signup and view all the answers

What happens to the depletion region when a reverse-bias voltage is applied?

It widens Signup and view all the answers

What is the characteristic of the initial flow of charge carriers when a reverse-bias voltage is applied?

It is transient Signup and view all the answers

What happens to the reverse current when the external reverse-bias voltage is increased to a certain value?

It drastically increases Signup and view all the answers

What is the current that flows when a forward bias is applied across a diode?

Forward current Signup and view all the answers

What happens to the forward current when the forward-bias voltage exceeds the diode's internal barrier voltage?

It increases rapidly Signup and view all the answers

What is the characteristic of the I-V curve for a diode in forward bias?

It is non-linear Signup and view all the answers

What is the characteristic of a diode when it is reverse-biased?

It blocks current except for a small leakage current Signup and view all the answers

What is the internal barrier voltage of a silicon diode?

0.7 volts Signup and view all the answers

What is the direction of the diffusion current ID?

From the p side to the n side Signup and view all the answers

What happens to the holes that diffuse across the junction into the n region?

They recombine with some of the majority electrons Signup and view all the answers

What is the result of the recombination process in the p region?

A region depleted of free holes Signup and view all the answers

What is the purpose of the built-in potential barrier across the PN junction?

To oppose the flow of holes and electrons Signup and view all the answers

What is the effect of applying a suitable positive voltage (forward bias) between the two ends of the PN junction?

It supplies the free electrons and holes with the extra energy Signup and view all the answers

What is the term for the current component due to electrons diffusing across the junction from the n side to the p side?

Jn Signup and view all the answers

What is the region close to the junction that is depleted of free electrons called?

Depletion region Signup and view all the answers

What happens to the free electrons that disappear from the n-type material due to recombination?

They disappear from the scene Signup and view all the answers

What happens when the reverse voltage across the diode becomes greater than its breakdown voltage point?

A sudden increase in reverse current occurs Signup and view all the answers

What is the primary reason for the choice of the arrow-like circuit symbol for a diode?

The diode conducts in one direction and not in the other Signup and view all the answers

What is the ideal behavior of a forward-biased diode?

It acts like a closed switch with zero voltage drop Signup and view all the answers

What happens when a diode is reverse-biased and the reverse bias voltage doesn't exceed the breakdown voltage of the junction?

The diode continues to block current flow Signup and view all the answers

What is the characteristic curve of a diode when the reverse voltage exceeds the breakdown voltage point?

A straight line downward curve Signup and view all the answers

What is the primary function of an ideal diode in a circuit?

To act as a switch and control current flow Signup and view all the answers

What is the term used to describe a forward-biased diode?

Turned on Signup and view all the answers

What is the main difference between a forward-biased and reverse-biased diode?

The direction of current flow Signup and view all the answers

Study Notes

Operation with Open-Circuit Terminals

Holes diffuse across the junction from the p side to the n side, while electrons diffuse across the junction from the n side to the p side, forming the diffusion current ID.
The direction of ID is from the p side to the n side.

Depletion Region

Holes that diffuse into the n region recombine with majority electrons, resulting in a region close to the junction depleted of free electrons.
Similarly, electrons that diffuse into the p region recombine with majority holes, resulting in a region close to the junction depleted of free holes.

Barrier Potential across PN Junction

A potential barrier exists across the junction, opposing the flow of holes and electrons.
The barrier potential is the energy required for electrons to pass through the depletion region.

Forward Bias

A suitable positive voltage (forward bias) applied between the two ends of the PN junction supplies free electrons and holes with extra energy, reducing the depletion region.
During forward bias, the energy loss results in a voltage drop across the PN junction equal to the barrier potential (0.7 V).

Reverse Bias

Reverse bias essentially prevents current through the diode.
Unlike charges attract, pulling majority carriers away from the PN junction, widening the depletion region and depleting majority carriers.
The reverse current is very small and can usually be neglected, but will drastically increase if the external reverse-bias voltage exceeds the breakdown voltage.

V-I Characteristic for Forward Bias

When forward bias is applied, the forward current and voltage across the diode gradually increase.
The curve increases gradually into the forward quadrant, but the forward current and voltage are extremely small until the forward voltage exceeds the diode's internal barrier voltage (0.7 V), at which point the forward current increases rapidly.

V-I Characteristic for Reverse Bias

The diode blocks current except for an extremely small leakage current, operating in the lower left quadrant of its I-V characteristic curves.
The diode continues to block current flow until the reverse voltage becomes greater than its breakdown voltage point.

Diode Models

Ideal diode model: conducts in one direction and not in the other.
Practical diode model: includes internal resistance and barrier potential.
Complete diode model: includes internal resistance, barrier potential, and breakdown voltage.

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Description

Learn about the diffusion current in semiconductor junctions, including the movement of holes and electrons across the p-n junction.