Paul Nunez1 Bruce Brunschwig1 Shu Hu2 Nathan Lewis1

1, California Institute of Technology, Pasadena, California, United States
2, Yale University, New Haven, Connecticut, United States

Electrical transport in amorphous titanium dioxide films deposited by atomic-layer deposition (ALD) and their heterostructures with p+-Si substrates have 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-voltage (J-V) characteristics. The comprehensive characterization reported herein, indicates a Ti3+ defect-mediated transport model: a hopping mechanism with a defect density of 1019 cm-3, defect band edge ~0.6 eV below the conduction band and a free carrier concentration of 1016 cm-3, which agrees with previous Hall measurements. Amorphous TiO2 films that were fabricated using TiCl4 as the ALD precursor exhibited less DC conductivity than films formed using tetrakis(dimethylamido)-titanium (TDMAT) as the precursor. The DC conductance increased proportionally to the peak height of the defect states in the valence band for TiCl4-precursor TiO2 films grown at 50°C, indicating that substantial room temperature conductivity is not intrinsic to amorphous TiO2 but is dependent on the introduction of defect states during the ALD fabrication process.