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Towards p-type conductivity in SnO2 nanocrystals through Li doping
Allen Chaparadza1, Shankar B Rananavare
1Department of Chemistry, Portland State University, Portland, OR 97207, USA. allc@pdx.edu
Nanotechnology
|December 8, 2009
Summary
Lithium-doped tin dioxide exhibits p-type conductivity, with electrical transport governed by variable range hopping mechanisms. Anomalous plateaus suggest a carrier inversion phenomenon at elevated temperatures.
Area of Science:
- Materials Science
- Solid-State Physics
- Semiconductor Physics
Background:
- Tin dioxide (SnO2) is a wide-bandgap semiconductor with applications in gas sensors and transparent conductive films.
- Doping SnO2 with lithium (Li) can modify its electrical and optical properties.
- Understanding charge transport mechanisms is crucial for optimizing semiconductor performance.
Purpose of the Study:
- To investigate the electrical transport properties of Li-doped SnO2 synthesized via sol-gel.
- To elucidate the role of Li ions and their dynamics within the SnO2 lattice.
- To explore the conduction mechanisms and potential carrier inversion phenomena.
Main Methods:
- Sol-gel synthesis of Li-doped SnO2.
- Solid-state 7Li Nuclear Magnetic Resonance (NMR) spectroscopy to study Li ion sites and dynamics.
- Variable-temperature direct current (dc) conductivity measurements.
- Analysis of conductivity data using Efros-Shklovskii (ES-VRH) and Mott (M-VRH) variable range hopping models.
Main Results:
- 7Li NMR confirmed Li ions occupy two distinct sites with different mobilities.
- Positive Seebeck coefficient indicated p-type conductivity in nanoparticulate films.
- DC conductivity showed a crossover from ES-VRH (below 100°C) to 2D Mott VRH (above 250°C).
- An anomalous temperature-independent resistivity plateau was observed in the transition region.
Conclusions:
- The observed hopping mechanisms (ES-VRH and M-VRH) are consistent with disordered semiconductor systems.
- The anomalous plateau is hypothesized to result from a carrier inversion, switching from holes to electrons.
- This carrier inversion is potentially driven by Li ion expulsion and oxygen vacancy formation at high temperatures, altering conductivity.
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