With prominent photocatalytic applications and widespread use in semiconductor devices, TiO2 is one of the most popular metal oxides. However, despite its popularity, it has yet to achieve its full potential due to a lack of effective methods for achieving p-type conductivity. Here, we show that undoped p-type TiO2 films can be fabricated by atomic layer deposition (ALD) and that their electrical properties can be controlled across a wide range using proper postprocessing anneals in various ambient environments. Hole mobilities larger than 400 cm(2)/(V·s) are accessible superseding the use of extrinsic doping, which generally produces orders of magnitude smaller values. Through a combination of analyses and experiments, we provide evidence that this behavior is primarily due to an excess of oxygen in the films. This discovery enables entirely new categories of TiO2 devices and applications, and unlocks the potential to improve existing ones. TiO2 homojunction diodes fabricated completely by ALD are developed as a demonstration of the utility of these techniques and shown to exhibit useful rectifying characteristics even with minimal processing refinement.

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Conductive nanowires (NWs) provide several advantages as a template and electrode material for solar cells due to their favorable light scattering properties. While the majority of NW solar cell architectures studied are based on semiconductor materials, metallic NWs could provide equivalent anti‐reflection properties, while acting as a low‐resistance back contact for charge transport, and facilitate light scattering in thin layers of semiconductors coated on the surface. However, fabrication of single‐crystalline highly anti‐reflective NWs on low‐cost, flexible substrates remains a challenge to drive down the cost of NW solar cells. In this study, metallic NixSi NW arrays are fabricated by a simple, bottom‐up, and low‐cost method based on the thermal decomposition of silane on the surface of flexible Ni foil substrates without the need for lithography, etching or catalysts. The optical properties of these NW arrays demonstrate broadband suppression of reflection to levels below 1% from 350 nm to 1100 nm, which is among the highest values reported for NWs. A simple route to control the diameter and density of the NWs is introduced based on variations in a carrier gas flow rate. A high‐resolution TEM, XRD and TEM‐EDS study of the NWs reveals that they are single crystalline, with the phase and composition varying between Ni2Si and NiSi. The nanowire resistivity is measured to be 10−4 Ω‐cm, suggesting their use as an efficient back electrode material for nanostructured solar cells with favorable light scattering properties.

Thin film capacitors of HfO2 with high energy storage were fabricated using plasma-enhanced atomic layer deposition on a relatively large platform with a lateral area of 0.8-7.1 mm2. An untreated film of 10-nm HfO2 showed a breakdown strength of 0.47 V/nm. Annealing of HfO2 formed a large crystalline phase, which creates electron paths and increases defect-induced currents. Laminate structures of Al2O3 and HfO2 were also fabricated to relate crystallinity, current leakage path, and breakdown behavior. A 7-layer laminate structure exhibited a breakdown strength of 0.58 V/nm with an aspect ratio of 1:300 000 due to suppressed crystallinity.

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