Question 1

What is the difference between p-type and n-type semiconductors?

Accepted Answer

P-type semiconductors are doped with acceptor atoms like boron or aluminum, which create holes as the dominant charge carriers. N-type semiconductors are doped with donor atoms like phosphorus or arsenic, which provide free electrons as the dominant charge carriers. Both types are created by adding impurities to pure silicon through a process called doping.

Question 2

How does doping improve the conductivity of a pure semiconductor?

Accepted Answer

Pure silicon atoms form covalent bonds with no free electrons, making them poor conductors. Doping adds impurities that either donate free electrons or create holes. These mobile charge carriers dramatically increase conductivity. Donor atoms contribute extra electrons, while acceptor atoms create positively charged holes that move through the lattice.

Question 3

What happens at the junction boundary in a p-n junction?

Accepted Answer

At the p-n junction boundary, electrons from the n-region diffuse toward the p-region, and holes from the p-region diffuse toward the n-region. This diffusion creates a depletion region with immobile positive and negative ions. The resulting electric field blocks current flow across the junction until an external voltage is applied.

Question 4

How does forward bias affect current flow through a diode?

Accepted Answer

Forward bias applies a positive voltage that reduces the depletion region width and weakens its electric field. This allows electrons and holes to jump across the junction, enabling current to flow through the diode. The current increases exponentially with applied voltage, as described by the Shockley diode equation.

Question 5

Why does a diode act as a one-way valve for electrical current?

Accepted Answer

A diode permits current flow in only one direction because of the depletion region's electric field. Forward bias reduces this field, allowing current to flow. Reverse bias increases the field strength and resistance, blocking current flow. Only a tiny saturation current leaks through when reverse biased, making the diode function as a valve.

Question 6

What are the practical applications of semiconductors in modern electronics?

Accepted Answer

Semiconductors form the foundation of all modern electronics. They are used to build diodes, transistors, and logic gates that perform Boolean operations like AND, OR, and NOT. These components enable digital addition, multiplication, and processor functions. Semiconductors also power light-emitting diodes for displays and communications technology.

Question 7

How do light-emitting diodes generate light from semiconductors?

Accepted Answer

An LED is a p-n junction that emits light when forward biased with suitable voltage. Electrons recombine with holes within the device, releasing energy in the form of light. LEDs made from semiconductors are more energy-efficient than incandescent bulbs and are widely used in environmental lighting, electronic displays, and advanced communications.

Semi-conducteurs

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