"Nano-In-Nano" Schottky Diodes Fabricated by Combining Self-Aligned Nanogap Patterning with Bottom-Up ZnO Nanowire Growth.

Nanoscale semiconductors offer significant advantages over their bulk semiconductor equivalents for electronic devices as a result of the ability to geometrically tune electronic properties, the absence of internal grain boundaries, and the very low absolute number of defects that are present in such small volumes of material. However, these advantages can only be realized if reliable contacts can be made to the nanoscale semiconductor using a scalable, low-cost process. Although there are many low-cost "bottom-up" techniques for directly growing nanomaterials, the fabrication of contacts at the nanoscale usually requires expensive and slow techniques like e-beam lithography that are also hard to scale to a level of throughput that is required for commercialization. A scalable method of fabricating such devices is demonstrated in this work by combining two bottom-up fabrication techniques. ZnO nanowire Schottky diodes are produced with a device length of a few tens of nanometers and a performance significantly exceeding a ZnO thin film equivalent. The first technique is adhesion lithography that allows self-aligned coplanar electrodes of different materials to be patterned with a nanogap ∼10 to 50 nm length between the two. In this case, one electrode is gold, while the other is a bilayer of titanium on a thin film of ZnO, and it is this thin film that allows the second technique, hydrothermal growth, to be used to grow ZnO nanowires directly across the nanogap. The resulting "nano-in-nano" Schottky diodes have a high rectification ratio >10, a low turn-on voltage <0.3 V, and a minimal off-state current <10 pA. This process could be used to realize a variety of nano-in-nano electronic devices in the future, including short channel gate-all-around (GAA) transistors.