Mott Variable Range Hopping

Definition

Mott Variable Range Hopping (VRH) is a mechanism of charge transport in disordered materials, particularly in organic semiconductors. This process involves hopping of charge carriers between localized states over variable distances, which allows for conduction even in materials that are not crystalline. The Mott VRH model highlights how temperature and the density of states affect charge mobility, making it a key concept in understanding how organic materials conduct electricity.

5 Must Know Facts For Your Next Test

1. Mott VRH is characterized by an exponential dependence of conductivity on temperature, indicating that as temperature increases, the hopping distance becomes more favorable for charge transport.
2. The activation energy for hopping in Mott VRH is related to the density of localized states available for charge carriers at the Fermi level.
3. In disordered materials, Mott VRH can dominate when the typical hopping distance exceeds the average distance between localized states, leading to enhanced conduction.
4. Mott VRH is often observed in organic semiconductors where structural disorder plays a significant role in determining electrical properties.
5. The Mott VRH model contrasts with the band theory of conductivity, where charges move through extended states rather than localized ones.

Review Questions

• How does Mott Variable Range Hopping explain charge transport in disordered organic materials compared to traditional band theory?
  • Mott Variable Range Hopping provides a framework for understanding charge transport in disordered organic materials by focusing on localized states instead of continuous energy bands. Unlike traditional band theory, which assumes that charge carriers can freely move through extended states, Mott VRH accounts for the significant impact of disorder on conductivity. In this context, charge carriers hop between localized states over varying distances depending on temperature and available energy states, allowing for conduction even in non-crystalline structures.
• Discuss the role of temperature in Mott Variable Range Hopping and how it affects the electrical conductivity of organic semiconductors.
  • Temperature plays a crucial role in Mott Variable Range Hopping by influencing the availability of localized states and the hopping process itself. As temperature increases, the thermal energy allows charge carriers to overcome energy barriers between localized states more easily. This results in an exponential increase in conductivity with temperature due to enhanced hopping probability over longer distances. Understanding this relationship helps explain why many organic semiconductors exhibit improved electrical performance at elevated temperatures.
• Evaluate the significance of Mott Variable Range Hopping in the design of organic electronic devices and its implications for future research.
  • The significance of Mott Variable Range Hopping in the design of organic electronic devices lies in its ability to explain and predict charge transport behavior in disordered materials. By recognizing that conductivity can be influenced by factors like localization and thermal activation, researchers can tailor material properties for specific applications such as organic photovoltaics or transistors. Future research may focus on optimizing organic materials to enhance Mott VRH characteristics, potentially leading to higher efficiency devices and novel applications in molecular electronics.

Related terms

Localized States: Energy states in a material where charge carriers can reside, often due to disorder or impurities, affecting charge transport.

Arrhenius Behavior: The temperature dependence of reaction rates, which can also apply to hopping mechanisms where conductivity increases with temperature.

Percolation Theory: A mathematical framework used to describe the movement and connectivity of particles through a medium, relevant for understanding how charges move through disordered materials.