MSc defense for Gor Nahapetyan

Title: Electrical and structural characterization of complex nanowire systems

Abstract: This thesis explores complex nanowire-based materials and devices, and is structured in two independent parts. The first part focuses on neuromorphic devices fabricated from InP and InAs nanowires.

We demonstrate on-chip optical communication between nanoscale components, including optical exci tation and inhibition of output light signals. These responses can be accurately modeled using sigmoid activation functions, reinforcing the relevance of these devices for photonic neural networks.

Further improvements are expected through capacitance optimization, backgate tuning of FET threshold voltages, and the fabrication of dedicated photoemitter nanowires. The second part centers on the structural characterization of phase-engineered InAsSb nanowires with epitaxially grown lead.

Using scanning transmission electron microscopy (STEM), we analyzed nanowires—grown externally—with controlled Sb content to induce crystal phase changes in the semiconductor core. A shadow junction was observed at the interface formed during lead deposition. Atomic-resolution imaging revealed that the orientation of lead grains may be influenced by phase transitions within the underlying nanowire.

These interfaces are atomically clean and well-defined, making the system promising for future investigations of transport phenomena in semiconduc tor–superconductor heterostructures.

Supervisor(s) Jesper Nygård, Joachim Sestoft