Final Report Summary - GUIDEDNW (Guided Nanowires: From Growth Mechanism to Self-Integrating Nanosystems)
Semiconductor nanowires are important building blocks for nanotechnology, but their large-scale assembly with controlled orientation on surfaces remains one challenge toward their integration into practical devices. In this project, we investigated the generality and applicability of a new approach for nanowire assembly based on in-plane growth guided by the substrate. We demonstrated the growth of perfectly aligned horizontal nanowires of a large variety of semiconductors (GaN, ZnO, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, PbSe, CsPbBr3) with controlled crystallographic orientations on different planes of various single-crystal substrates (sapphire, quartz and spinel). The growth directions and crystallographic orientation of the nanowires were found to be controlled by their epitaxial relationship with the substrate, as well as by a graphoepitaxial effect that guides their growth along surface steps and grooves. Guided nanowires were also grown by artificial epitaxy on lithographically patterned amorphous substrates (oxidized silicon wafers). This makes guided growth compatible with traditional silicon-based microelectronics and microelectromechanical systems as a hybrid technology . We have developed new analytical methods to optically determine and map the crystallographic orientation of the guided nanowires. We have also studied the kinetics of guided nanowire growth and developed a theoretical model that successfully describes and predicts their geometric scaling. Guided nanowires enabled the controlled growth of nanowires with complex morphologies and heterostructures and their self-integration into a variety of nanoelectronic and nano-optoelectronic devices, including logic circuits, fast and sensitive photodetectors in different ranges of the electromagnetic spectrum from UV through the visible to IR, and photovoltaic cells based on core-shell nanowires of n-type and p-type semiconductors (ZnSe@ZnTe, CdS@CdSe, CdS@Cu2S). Arrays of these core-shell nanowires were integrated in series to produce micro-photovoltaic cells capable to supplying high voltages in reduced dimensions, as needed for future technologies, such as the powering of sensor network nodes for the internet of things. This development led to the filing of one patent named PHOTOVOLTAIC DEVICES BASED ON GUIDED NANOWIRE ARRAYS, and a granted Proof-of-Concept (PoC) ERC project titled High-Voltage Micro-Photovoltaic Cells and Photodetectors Based on Guided Nanowires for On-Chip Powering of Autonomous Microsystems.