Physics: Semiconductos Quiz

📝 Special Statement

What Are Semiconductors?

Semiconductors are materials that have a conductivity somewhere between a conductor (which conducts electricity well) and an insulator (which does not). Their key property is that their conductivity can be easily changed by introducing impurities, a process called doping, or by changing their temperature. The most common examples are silicon (Si) and germanium (Ge).

Understanding Energy Bands

To understand semiconductors, you need to know about energy bands.

• Valence Band: This is the highest energy band that is completely filled with electrons at a temperature of absolute zero (0 K). Electrons in this band are bound to the atoms and cannot move freely.
• Conduction Band: This is the next highest energy band. It is typically empty at 0 K. Electrons in this band are free to move and conduct electricity.
• Band Gap: This is the energy difference between the valence band and the conduction band. For a material to conduct electricity, an electron must gain enough energy to jump across this gap from the valence band to the conduction band.

Types of Semiconductors

There are two main types of semiconductors:

Intrinsic Semiconductors

These are pure semiconductors, like pure silicon. At 0 K, they act as insulators because the valence band is full and the conduction band is empty. At room temperature, some electrons gain enough thermal energy to jump the band gap, leaving behind a hole in the valence band. Both the free electron and the hole can act as charge carriers, but their numbers are very limited, leading to low conductivity.

Extrinsic Semiconductors

These are semiconductors that have been doped to increase their conductivity. Doping involves adding a small amount of an impurity (a different element) to the pure semiconductor. This creates two subtypes:

• N-Type Semiconductor: This is created by doping a pure semiconductor with a pentavalent impurity (an element with 5 valence electrons, like phosphorus). The extra electron from the impurity is not needed for bonding and becomes a free electron, which acts as the majority carrier. The name "N-type" comes from the negative charge of the electrons.
• P-Type Semiconductor: This is created by doping a pure semiconductor with a trivalent impurity (an element with 3 valence electrons, like boron). The impurity atom creates a "hole" in the crystal structure, which acts as a positive charge carrier. These holes are the majority carriers. The name "P-type" comes from the positive charge of the holes.

The P-N Junction

When a P-type and an N-type semiconductor are joined together, they form a p-n junction. This junction is the foundation of many electronic devices like diodes and transistors.

• Depletion Region: At the junction, free electrons from the N-side diffuse into the P-side, filling the holes. This creates a region around the junction that is "depleted" of mobile charge carriers. This region has a built-in potential barrier that prevents further flow.
• Forward Bias: When an external voltage is applied to the p-n junction with the positive terminal on the P-side and the negative terminal on the N-side, it reduces the potential barrier. This allows majority carriers to flow across the junction, resulting in a large current.
• Reverse Bias: When the external voltage is applied with the positive terminal on the N-side and the negative terminal on the P-side, it increases the potential barrier. This prevents the flow of majority carriers, and only a very small leakage current flows.

📋 Instructions