Characterization of Electronic Transport through Amorphous TiO2 Produced by Atomic-Layer Deposition

Paul Nunez, Matthias Richter, Brandon Piercy, Christopher Roske, Miguel Caban-Acevedo, Mark Losego, Steven Konezny, David Fermin, Shu Hu, Bruce Brunschwig, Nathan Lewis

Research output: Contribution to journalArticle (Academic Journal)peer-review

17 Citations (Scopus)
14 Downloads (Pure)

Abstract

The electrical transport in amorphous titanium dioxide (a-TiO2) thin films deposited by atomic-layer deposition (ALD), and across heterojunctions of p+-Si|a-TiO2|metal substrates that had various top metal contacts, has been characterized by AC conductivity, temperature-dependent DC conductivity, space-charge-limited current (SCLC) spectroscopy, electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), and current density versus voltage (J-V) characteristics. Amorphous TiO2 films were fabricated using either tetrakis(dimethylamido)-titanium (TDMAT) with a substrate temperature of 150 °C or TiCl4 with a substrate temperature of 50, 100, or 150 °C. EPR spectroscopy of the films showed that the Ti3+ concentration varied with the deposition conditions, and increases in the concentration of Ti3+ in the films correlated with increases in film conductivity. Valence-band spectra for the a-TiO2 films exhibited a defect-state peak below the conduction-band minimum (CBM), and increases in the intensity of this peak correlated with increases in the Ti3+ concentration measured by EPR as well as with increases in film conductivity. The temperature dependent conduction data showed Arrhenius behavior at room temperature with an activation energy that decreased with decreasing temperature, suggesting that conduction did not occur primarily through either the valence or conduction bands. The data from all of the measurements are consistent with a Ti3+ defect-mediated transport mode involving a hopping mechanism with a defect density of 1019 cm-3, a 0.83 wide defect-band centered 1.47 eV below the CBM, and a free-electron concentration of 1016 cm-3. The data are consistent with substantial room-temperature anodic conductivity resulting from introduction of defect states during the ALD fabrication process as opposed charge transport intrinsically associated with the conduction band of TiO2.
Original languageEnglish
Pages (from-to)20116 - 20129
Number of pages14
JournalJournal of Physical Chemistry C
Volume123
Issue number33
DOIs
Publication statusPublished - 19 Jun 2019

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