Hybrid Heterostructure Nanowires

Semiconductor nanowires are a promising geometry for next-generation electronic devices, exploiting the reduced density of states and quantization effects and allowing higher transit frequencies at reduced leakage currents. Additionally, the large surface to volume ratio makes them an ideal candidate for chemical sensing applications or for photovoltaic energy conversion. All these applications benefit from the wide selection of materials, which can be integrated onto the e.g. Si/Ge platform by using epitaxially grown nanowires. Their functionality can be extended further through semiconductor heterostructures, which allow to design the electronic structure for specific applications. The main goal of this project is the fabrication, characterization and optimization of hybrid nanowire heterostructures, consisting of Si/Ge and III-V materials. The small contact area between substrate and nanowire or between two nanowires provides the ability to join materials with different lattice-constant and chemical bonding together and characterize these heterojunctions in an unstrained and defect-free case. In particular, we will investigate the growth of III-V nanowires on Si/Ge nanowires and vice versa. Until now most research work was concentrating on Si/Ge or III-V nanowire heterostructures, therefore the approach to integrate both material groups is a logical consequence. The novelty of such structures requires efforts to establish the epitaxial growth and characterize these hybrid nanowires structurally, optically and electronically. Possible approaches, which are point of investigation in this project, are axial Si/Ge/III-V heterostructures, III-V branches on Si/Ge nanowires and the growth of Si/Ge structures on III-V nanowires. Finally, the combination of all these techniques will allow the fabrication of Si/Ge/III-V nanowire heterostructures with multiple interfaces and III-V quantum dots, embedded into group IV nanowires. For this purpose, we will also investigate novel catalysts for improved heterostructure growth and electrical contacts. The electronic properties of these heterostructures will be investigated by optical experiments and electronic transport studies on single nanowires and small ensembles. This project will therefore provide a way to integrate the flexibility and functionality of III-V heterostructures with Si/Ge established device technology. As these are novel structures, a further goal is the development of prototype devices, which are based on nanowire heterostructures, but allow the integration with planar device geometries. We propose different device geometries, which will allow the integration of epitaxially grown III-V or hybrid nanowires with conventional Si/Ge device fabrication techniques. These devices will be based on silicon-on-insulator substrates, where nanowires will be grown in place without the need for harvesting, positioning and contacting dispersed wires. These will allow to make the transition from growth and material characterization towards functional electronic or optoelectronic devices, which then can be developed further, focusing specific applications.

No additional funding sources recorded.