Séminaire Rainer Timm- 15 Octobre 2019 - Semiconductor nanowires for advanced devices: surface and structure characterization at the atomic scale

Invitation : Thomas Cornelius (Département PHANO, Equipe MNO).

Diffusion : IM2NP, CINaM, Irphe, LP3, Madirel (via P. Boulet), PIIM (via T. Angot), CPT (T. Martin), Fédération de Chimie (via S. Viel), CP2M

SEMINAIRE Mardi 15 octobre 2019 à 11h00

Salle des séminaires de l'Im2np, campus de Saint-Jérôme, aile 1, niveau 6 service 161

Rainer Timm

Synchrotron Radiation Research and NanoLund, Lund University, Sweden

Semiconductor nanowires for advanced devices:

surface and structure characterization at the atomic scale

Semiconductor nanowires are promising candidates for next generation (opto)electronic devices. They come along with novel materials science properties, and they allow a large flexibility in combining different materials. As an example, III-V semiconductor nanowires with superior charge carrier mobility and direct bandgap can be epitaxially grown on silicon substrates without interfacial defects, enabling ultrafast and low-power tunnel field effect transistors or solar cells with high efficiency at moderate costs. In order to improve device performance and realize novel applications, it is desirable to investigate individual nanowires during device operation. Furthermore, due to their small size and high aspect ratio, properties of nanowire-based devices are to a significant extend determined by surface effects. Therefore, surface and interface characterization at the atomic scale is essential.

Here, I will present our toolbox for characterizing crystal structure and atomic surface properties of semiconductor nanowires. Using scanning tunneling microscopy and spectroscopy (STM/S), we map nanowire heterostructures across interfaces between different crystal phase, different doping, or different materials, correlating atomic surface structure with changes in electronic properties at the sub-nm scale. This includes in-situ and operando studies, where we investigate InAs/GaSb nanowires during device performance or while their surface becomes modified, complemented by X-ray photoemission spectroscopy studies for evaluating changes in chemical composition. Simultaneous STM/S and electrical transport studies show a significant difference between nanowire surface and bulk properties. Finally, we use nano X-ray diffraction and coherent diffraction imaging for correlating structural properties of individual nanowires with their electrical performance and for monitoring the strain distribution inside a nanowire as a result of device processing.