I have found that ZnO thin films show either metallic or insulate behaviours when annealed at 700OC in vacuum and ambient atmospheres respectively, and am looking for help explaining this phenomena. Most literature only covers ZnO annealed at temperatures of 350OC so I'm having difficulty explaining this phenomena when annealed at such high temperatures.
To elaborate on my difficulty, I am attempting to fabricate ZnO/Bi4Ti3O12 Metal-Ferroelectric-semiconductor devices on insulative Al2O3 substrates. ZnO films are deposited directly onto Si2O3 substrates by RF magnetron sputtering, followed shortly by the BTO thin films. The devices are then annealed at 700OC for 1 hour to crystallise the BTO thin film. One batch of samples were annealed in ambient atmosphere, another in vacuum to study the annealing atmosphere effect.
During C-V measurements I found only noise level capacitance in devices annealed in vacuum suggesting the ZnO had become insulative. The C-V behaviours of the vacuum annealed sample however showed regular capacitor behaviours, indicating the metallic like conductivity.
I understand that the electrical conductivity in un-doped ZnO thin films derives from oxygen vacancies. I have theorised that the high annealing temperature of 700OC would either significantly deplete the oxygen vacancies causing insulative behaviours in vacuum, or increases there number resulting in metallic like conductivity in vacuum, however I have not been able to find any literature covering the annealing of ZnO thin films deposited by RF-magnetrons puttering in this manner.
Any help, literature, or insight people can provide would be greatly appreciated.
Many thanks
David Coathup
There are some mechanism in the article and references about the medium effect of TiO2, I am not sure but might be helpful.
https://www.researchgate.net/publication/311977968_Accelerated_formation_of_BaTiO3_ceramics_with_mechanochemical_processing_in_different_liquids
Article Accelerated formation of BaTiO3 ceramics with mechanochemica...
Thank you for your input. I am more concerned with the conduction methods in the ZnO thin film more than I am in the Bi4Ti3O12 layer at the moment.
There is a few article about the atmospheres. I sent my articles because the electrical properties change with atmospheres and maybe some references could be useful.
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