Question

The intrinsic semi-conductor has : (A) a finite resistance which does not change with temperature (B) infinite resistance which decreases with temperature (C) Finite resistance which decreases with temperature (D) Finite resistance which does not change with temperature

Short answer

The correct answer is (C) Finite resistance which decreases with temperature, because the resistance of an intrinsic semiconductor depends on the number of charge carriers, which in turn depend on the temperature. As the temperature increases, the number of charge carriers increases, resulting in a decrease in resistance.

Step-by-step solution

Recall properties of intrinsic semiconductors

An intrinsic semiconductor is a pure semiconductor material that has no impurities or dopants. At low temperatures, its charge carriers (electrons and holes) are in limited supply, and as the temperature increases, the number of charge carriers also increases. Since the resistance of a semiconductor is inversely proportional to the number of charge carriers, an increase in charge carriers will result in a decrease in resistance.

Relate the resistance to temperature

As we have understood that the resistance of an intrinsic semiconductor depends on the number of charge carriers, which in turn depend on the temperature, we can conclude that the resistance of an intrinsic semiconductor will vary with temperature.

Identify the correct option

Given the above conclusions: (A) and (D) are incorrect because the resistance of an intrinsic semiconductor changes with temperature. (B) is incorrect because intrinsic semiconductors have finite resistance, not infinite resistance. The correct answer is: (C) Finite resistance which decreases with temperature.

Key concepts

Temperature Dependence of Resistance

In intrinsic semiconductors, the resistance is a crucial property that changes with temperature. Let's explore why. At a fundamental level, resistance is determined by how easily current can flow through a material. For semiconductors, the flow of current is carried by "charge carriers," which are electrons and holes.

As the temperature of an intrinsic semiconductor increases, more thermal energy becomes available. This energy helps electrons leap across the energy gap from the valence band to the conduction band, creating more charge carriers. When more electrons jump to the conduction band, additional holes are left behind in the valence band.

This increase in the number of charge carriers leads to a significant decrease in resistance. In simple terms, more carriers mean a higher potential for current flow, making it easier for electricity to move through the material. Thus, intrinsic semiconductors display a "finite resistance which decreases with temperature." Understanding this relationship is essential when considering how semiconductor devices react under different temperature conditions.

Charge Carriers

Charge carriers are the backbone of how current travels through a semiconductor. In intrinsic semiconductors, these carriers are naturally occurring due to inherent properties of the material without any impurities.

There are two primary types of charge carriers in semiconductors:

• Electrons: These are negatively charged particles that move through the conduction band.
• Holes: These are essentially a lack of an electron, acting like a positive charge in the valence band.

As temperature increases, more electrons gain enough energy to move from the valence to the conduction band, leaving behind "holes." This increase in electrons and holes means more charge carriers are available, which determines the semiconductor's conductivity.

Therefore, the number of charge carriers in an intrinsic semiconductor directly influences how effectively it can conduct electricity. More carriers at higher temperatures contribute to reduced resistance, facilitating better conductivity.

Intrinsic Semiconductor Properties

Intrinsic semiconductors are unique because they rely entirely on their natural structure to conduct electricity. Made from pure semiconductor materials such as silicon or germanium, they have distinctive properties that set them apart from other types of semiconductors.

Some of these key properties include:

• Purity: Without any dopants or impurities, these materials depend solely on electron-hole pairs to conduct electricity.
• Temperature Sensitivity: Their electrical properties change significantly with temperature variation. Besides affecting the resistance, temperature also impacts the concentration of charge carriers.
• Energy Band Gap: The band gap in intrinsic semiconductors is typically small enough to allow electrons to jump from the valence to the conduction band as temperature increases. This process generates more charge carriers.

These properties are vital for understanding the intrinsic semiconductor's ability to conduct electricity. As their resistance decreases with temperature, intrinsic semiconductors become more conductive, adapting to changes in their environment in a way that doped semiconductors do not.