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Mott and Efros-Shklovskii variable range hopping in CdSe quantum dots films
Heng Liu1, Alexandre Pourret, Philippe Guyot-Sionnest
1James Franck Institute, The University of Chicago, 929 E. 57th Street Chicago, Illinois 60637, USA.
ACS Nano
|August 20, 2010
Summary
Variable range hopping conductivity in cadmium selenide colloidal quantum dot solids exhibits a crossover between Mott and Efros-Shklovskii models. This transition depends on the density of states, confirmed via electrochemical tuning.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Nanotechnology
Background:
- Variable range hopping (VRH) describes charge transport in disordered systems.
- Mott and Efros-Shklovskii (ES) models predict different temperature dependencies for VRH conductivity.
- Colloidal quantum dots offer tunable electronic properties for studying charge transport mechanisms.
Purpose of the Study:
- To experimentally investigate the crossover between Mott and Efros-Shklovskii VRH conductivity models.
- To explore the influence of the density of states on conductivity in 3D quantum dot solids.
- To validate VRH models for non-Ohmic conductivity in cadmium selenide (CdSe) quantum dots.
Main Methods:
- Fabrication of 3D solids from monodispersed CdSe colloidal quantum dots.
- Electrochemical tuning of the density of states at the Fermi level.
- Temperature-dependent conductivity measurements.
- Analysis of conductivity exponents (1/4 for Mott, 1/2 for ES).
Main Results:
- Observed a crossover in conductivity behavior consistent with Mott and ES VRH models.
- Mott hopping (1/4 exponent) observed at low density of states (<0.4e(-)/dot) and in the conductivity gap (2e(-)/dot).
- Efros-Shklovskii hopping (1/2 exponent) observed at higher charge fillings (up to 6e(-)/dot).
- Non-Ohmic conductivity quantitatively explained by the VRH model.
Conclusions:
- The density of states critically governs the VRH conductivity mechanism in CdSe quantum dot solids.
- Electrochemical control provides a versatile method to tune and study charge transport in nanomaterials.
- The VRH model accurately describes conductivity across various charge densities and non-Ohmic regimes.
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