Browse/search for people

Publication - Professor David Fermin

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

    Citation

    Nunez, P, Richter, M, Piercy, B, Roske, C, Caban-Acevedo, M, Losego, M, Konezny, S, Fermin, D, Hu, S, Brunschwig, B & Lewis, N, 2019, ‘Characterization of Electronic Transport through Amorphous TiO2 Produced by Atomic-Layer Deposition’. Journal of Physical Chemistry C, vol 123., pp. 20116 - 20129

    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.

    Full details in the University publications repository