Distinguishing between deep trapping transients of electrons and holes in TiO2 nanotube arrays using planar microwave resonator sensor

• Author(s) / Creator(s)

  • Mohammad H Zarifi, Benjamin Daniel Wiltshire, Najia Mahdi, Karthik Shankar, Mojgan Daneshmand

• A large signal direct current (DC) bias and a small signal microwave bias were simultaneously applied to TiO2 nanotube membranes mounted on a planar microwave resonator. The DC bias modulated the electron concentration in the TiO2 nanotubes, and was varied between 0 and 120 V in this study. Transients immediately following the application and removal of DC bias were measured by monitoring the S-parameters of the resonator as a function of time. The DC bias stimulated Poole-Frenkel type trap-mediated electrical injection of excess carriers into TiO2 nanotubes which resulted in a near constant resonant frequency but a pronounced decrease in the microwave amplitude due to free electron absorption. When ultraviolet illumination and DC bias were both present and then step-wise removed, the resonant frequency shifted due to trapping -mediated change in the dielectric constant of the nanotube membranes. Characteristic lifetimes of 60-80 s, 300−800 s and ~3000 s were present regardless of whether light or bias was applied and were also observed in the presence of a hole scavenger, which we attributed to oxygen adsorption and deep electron traps while another characteristic lifetime > 8000 s was only present when illumination was applied, and is attributed to the presence of hole traps.

• Date created

  2018-05-11

• Subjects / Keywords

  • carrier dynamics
  • electrochemical anodization
  • photodielectric effect
  • photoconductivity

• Type of Item

  Article (Published)

• DOI

  https://doi.org/10.7939/r3-mva9-5t02

• License

  Attribution-NonCommercial 4.0 International