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Reappraisal of variable-range hopping in quantum-dot solids
Arjan J Houtepen1, Daan Kockmann, Daniël Vanmaekelbergh
1Condensed Matter and Interfaces, Debye Institute, Utrecht University, PO Box 80.000, 3508 TA Utrecht, The Netherlands. a.j.houtepen@tudelft.nl
Nano Letters
|September 16, 2008
Summary
Electrical conductivity in zinc oxide (ZnO) nanocrystals follows a unique temperature dependence, unexplained by current models. A modified hopping model accurately describes this behavior across various conditions.
Area of Science:
- Condensed matter physics
- Materials science
- Nanotechnology
Background:
- Electrical conductivity in nanomaterials is crucial for electronic applications.
- Existing models fail to explain the observed temperature dependence in ZnO nanocrystals.
- Previous studies on gold (Au) nanocrystals showed similar anomalous behavior.
Purpose of the Study:
- To investigate the temperature dependence of electrical conductivity in zinc oxide (ZnO) nanocrystal assemblies.
- To develop a theoretical model that accurately describes the experimental findings.
- To understand the underlying charge transport mechanisms in ZnO nanocrystals.
Main Methods:
- Utilizing an electrochemically gated transistor setup to study ZnO nanocrystal assemblies.
- Analyzing the temperature dependence of electrical conductivity from 7 to 200 K.
- Adapting the Efros-Shklovskii variable-range hopping model.
Main Results:
- The electrical conductivity exhibited a precise temperature dependence described by ln sigma = ln sigma0 - (T0/T)(x) with x=2/3.
- This relationship held true across the entire temperature range, irrespective of charge concentration or dielectric environment.
- The proposed model, incorporating nonresonant tunneling via local energy fluctuations, successfully explained the experimental observations.
Conclusions:
- The study reveals a novel charge transport mechanism in ZnO nanocrystals.
- The adapted Efros-Shklovskii model provides a robust explanation for the observed temperature dependence.
- Findings offer insights into the fundamental physics governing charge transport in disordered nanomaterials.
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