Understanding the Unique Behavior of Semiconductor Resistance at Elevated Temperatures

When discussing the behavior of resistance in materials, the fundamental differences between conductors and semiconductors are often overlooked. This article delves into the unique mechanisms and properties of semiconductors that explain why the resistance changes in a way that is fundamentally different from metals as temperature increases.

Resistance in Semiconductors

The behavior of resistance in semiconductors, such as silicon, is fundamentally different from that of conductors like metals. The key difference lies in the nature of their charge carriers and how they respond to temperature changes.

Conductors, like metals, have a high density of free electrons that facilitate electrical conduction. As temperature increases, the thermal vibrations of the lattice structure intensify, causing more collisions between electrons and the lattice, which increases resistance.

In contrast, semiconductors have fewer charge carriers at low temperatures. However, as temperature rises, more electrons gain enough energy to jump from the valence band to the conduction band, increasing the number of free charge carriers (electrons and holes) available for conduction.

Temperature Effect in Semiconductors

The effect of temperature on the resistance of semiconductors is a bit more complex. At high temperatures, two opposing effects come into play:

Increased Carrier Concentration: More electrons are promoted to the conduction band, which decreases resistance. Increased Lattice Vibrations: Higher temperatures lead to more lattice vibrations, causing more collisions and increasing resistance.

However, the increase in charge carriers typically outweighs the increased lattice vibrations, leading to a decrease in resistance as temperature increases for most intrinsic semiconductors.

Why Not the Same Theory as Conductors

The reasons why the theory of resistance applied to conductors does not hold for semiconductors are rooted in different mechanisms of conduction and intrinsic vs. extrinsic properties.

Different Mechanisms of Conduction

In conductors, the primary mechanism of conduction involves free electrons in a fixed lattice structure. Resistance is mainly influenced by electron scattering due to lattice imperfections and thermal vibrations.

In semiconductors, conduction involves both electrons and holes, and the number of available charge carriers changes with temperature. This complexity makes the resistance behavior more intricate.

Intrinsic vs. Extrinsic Properties

Semiconductors can be doped to create extrinsic properties, such as n-type or p-type. This doping can significantly affect how temperature impacts resistance, which is not a factor in typical metallic conductors.

Non-linear Behavior

The relationship between temperature and resistance in semiconductors often exhibits a non-linear behavior. In some cases, semiconductors can exhibit negative temperature coefficient (NTC) resistance, meaning resistance decreases with increasing temperature.

Summary

While the resistance of conductors generally increases with temperature due to increased scattering of charge carriers, the resistance of semiconductors typically decreases with increasing temperature due to the significant increase in charge carrier density. These underlying mechanisms lead to different behaviors in response to temperature changes, making it crucial to understand and apply the appropriate theories based on the material type.

In conclusion, semiconductor resistance at elevated temperatures behaves in a unique manner compared to conductors, and this understanding is vital for a range of applications from electronics to energy conversion, where temperature effects can significantly impact performance.