We have developed a low-temperature atomic layer deposition (ALD) process for depositing crystalline and phase pure spinel cobalt oxide (Co3O4) films at 120 °C using [Co(tBu2 DAD)2] and ozone as co-reagent. X-ray diffraction, UV-Vis spectroscopy, atomic force microscopy, field emission scanning electron microscopy, X-ray photoelectron spectroscopy and time-of-flight elastic recoil detection analysis were performed to characterize the structure and properties of the films. The as-deposited Co3O4 films are crystalline with low amount of impurities (<2 % C and <5 % H) despite low deposition temperatures. Deposition of Co3O4 onto thin TiO2 photoanodes (100 nm) for water oxidation resulted in 30 % improvement of photocurrent (after 10 ALD cycles yielding small Co3O4 particles) as compared to pristine TiO2 films), and exhibited no detrimental effects on photocurrent response up to 300 deposition cycles (approximately 35 nm thick films), demonstrating the applicability of the developed ALD process for deposition of effective catalyst particles and layers in photoelectrochemical water-splitting devices.
High-performance p-type oxide thin film transistors (TFTs) have great potential for many semiconductor applications. However, these devices typically suffer from low 1 hole mobility and high off-state currents. We fabricated p-type TFTs with a phasepure polycrystalline Cu 2 O semiconductor channel grown by atomic layer deposition (ALD). The TFT switching characteristics were improved by applying a thin ALD Al 2 O 3 passivation layer on the Cu 2 O channel, followed by vacuum annealing at 300 • C. Detailed characterisation by TEM-EDX and XPS shows that the surface of Cu 2 O is reduced following Al 2 O 3 deposition and indicates the formation of 1-2 nm thick CuAlO 2 interfacial layer. This, together with field-effect passivation caused by the high negative fixed charge of the ALD Al 2 O 3 , leads to an improvement in the TFT performance by reducing the density of deep trap states as well as by reducing the accumulation of electrons in the semiconducting layer in the device off-state.
Herein, we report an atomic layer
deposition (ALD) process for
Cu
2
O thin films using copper(II) acetate [Cu(OAc)
2
] and water vapor as precursors. This precursor combination enables
the deposition of phase-pure, polycrystalline, and impurity-free Cu
2
O thin films at temperatures of 180–220 °C. The
deposition of Cu(I) oxide films from a Cu(II) precursor without the
use of a reducing agent is explained by the thermally induced reduction
of Cu(OAc)
2
to the volatile copper(I) acetate, CuOAc. In
addition to the optimization of ALD process parameters and characterization
of film properties, we studied the Cu
2
O films in the fabrication
of photoconductor devices. Our proof-of-concept devices show that
approximately 20 nm thick Cu
2
O films can be used for photodetection
in the visible wavelength range and that the thin film photoconductors
exhibit improved device characteristics in comparison to bulk Cu
2
O crystals.
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