TY - JOUR
T1 - Characterization of Electronic Transport through Amorphous TiO2 Produced by Atomic-Layer Deposition
AU - Nunez, Paul
AU - Richter, Matthias
AU - Piercy, Brandon
AU - Roske, Christopher
AU - Caban-Acevedo, Miguel
AU - Losego, Mark
AU - Konezny, Steven
AU - Fermin, David
AU - Hu, Shu
AU - Brunschwig, Bruce
AU - Lewis, Nathan
PY - 2019/6/19
Y1 - 2019/6/19
N2 - 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.
AB - 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.
U2 - 10.1021/acs.jpcc.9b04434
DO - 10.1021/acs.jpcc.9b04434
M3 - Article (Academic Journal)
SN - 1932-7447
VL - 123
SP - 20116
EP - 20129
JO - Journal of Physical Chemistry C
JF - Journal of Physical Chemistry C
IS - 33
ER -