Andrei T. Iancu

Atomic Layer Deposition of Undoped TiO2 Exhibiting p-Type Conductivity

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.

High aspect ratio and high breakdown strength metal-oxide capacitors

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.