Variable range hopping conduction in ZnO nanocrystal thin films.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Zinc oxide (ZnO) nanocrystal films are investigated for thin film transistors and transparent conductive oxides.
• Previous research focused on highly conductive ZnO films, leaving the insulating to semi-insulating regime less explored.
• Understanding defect and surface states in ZnO nanocrystal interfaces is crucial for advanced electronic applications.

Purpose of the Study:

• To investigate the insulating to semi-insulating regime of zinc oxide (ZnO) nanocrystal films.
• To explore the impact of post-deposition treatments on the electrical properties of ZnO nanocrystal films.
• To gain deeper insights into surface states and defect states at nanocrystal interfaces.

Main Methods:

• Examined effects of post-deposition treatments: UV light exposure, atomic layer deposition matrix filling, and thermal annealing.
• Observed Mott and Efros-Shklovskii variable range hopping conduction mechanisms.
• Determined Fermi level density of states and electron localization length by transitioning between conduction mechanisms.

Main Results:

• Post-deposition treatments were used to transition ZnO nanocrystal films between Mott and Efros-Shklovskii variable range hopping regimes.
• The study determined the Fermi level density of states and electron localization length.
• A model was proposed where ZnO nanocrystals have quasi-neutral cores and shells depleted by surface OH trap states.

Conclusions:

• Post-treatments primarily enhance conductivity by reducing the distance between quasi-neutral nanocrystal cores, improving inter-nanocrystal tunneling.
• The proposed model explains the conductivity changes in ZnO nanocrystal films based on surface states and core-shell structure.
• This research provides a pathway to control the electronic properties of ZnO nanocrystal films for specific applications.