EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The formation of III-V semiconductor nanowire (NW) heterostructures as building blocks for advanced electronic and optoelectronic devices is a major goal of the NW community. However, strategies to realise complex III-V semiconductor NW heterostructures solely by the metal-assisted growth and going beyond the axial arrangement of the segments are rare. In this contribution, we report the...

Selective area epitaxy of semiconductor heterostructures takes place on a crystal inside predefined patterns obtained by lithography inside an oxide mask. This technique allows the growth of complex structures which are highly scalable. As a typical example, we will consider InGaAs nanowire networks grown on InP. Based on physical information obtained from scanning probe microscopies, such as...

Assembling nanostructured building blocks into network materials unlocks macroscopic properties inaccessible with monolithic solids. Recently we were able to show that silicon nanowires (SiNWs) can be produced via floating catalyst chemical vapor deposition (FCCVD), a method that enables large-scale and continuous synthesis of SiNWs suspended in the gas phase exploiting metal-catalized...

Aerotaxy is a unique technique to grow nanowires in a continuous gas flow without a substrate[1]. Controlled dopant levels have been demonstrated in this technique to high concentrations[2]. Recently, we have used high-throughput techniques to reveal the relationship between internal quantum efficiency and Zn-doping in GaAs[3], a crucial parameter to determine the nanowire performance.

In...

Short-period superlattices have diverse functionality in electronic and optoelectronic devices. Implementing such systems as axial heterostructures in freestanding semiconducting nanowires further broadens the scope of potential applications, for example: distributed Bragg reflectors, high-efficiency light-emitting diodes, and quantum dot heterostructures. The challenge, however, lies in...

III-V semiconductor nanowires (NWs) obtained by the vapor-liquid-solid (VLS) mechanism exhibit a zinc-blende (ZB) or a wurtzite (WZ) structure [1] depending on the growth conditions, and more particularly on the amount of III and V element fluxes [2-4]. Controlling precisely the growth of the crystal phases of self-assisted GaAs NWs by molecular beam epitaxy (MBE) would be an important...

Networks of interconnected semiconductor nanowires (NWs) are essential elements to study fundamental quantum phenomena such as Majorana-mode braiding, quantum interference, multi-terminal Josephson junctions, and the superconductor-insulator transition [1]. Selective-area growth (SAG) is a promising technique to realize such networks on-demand allowing ultimate scalability. Narrow-bandgap...

The combination of core-shell geometry and band gap engineering in nanowire (NW) heterostructures can be employed to realize systems with novel transport and optical properties. The InAs/GaSb material system is particularly interesting because of the very low lattice-mismatch (0.6%), broken-gap band alignment (type-III), and small effective masses of electrons and holes in InAs and GaSb...

One-dimensional inorganic nanotubes hold promise for technological applications due to their distinct physical/chemical properties, but so far advancements have been hampered by difficulties in producing single-wall nanotubes with a well-defined radius. In this work, we investigate, based on Density Functional Theory (DFT), the formation mechanism of 135 different inorganic nanotubes formed by...

Mid-infrared (MIR) light sources have been demanded for sensing applications because MIR absorptions are finger prints of various materials. In particular, MIR lasers based on nanomaterials have recently attracted attention for device integration. The MIR nanolaser was achieved using InAs and PbS nanowires at wavelengths of 2.6 and 3 μm, respectively [1, 2]. Black phosphorus, which is a...

Telecom-band nanowire lasers [1-3] based on III-V materials require continuous-wave (CW) operation at room temperature for future photonic on-chip processors. However, most of the nanowire lasers reported so far have been operated under pulse-pumping conditions, and the few that have shown CW lasing did so only at cryogenic temperatures. The critical issue to hinder room-temperature CW lasing...

Compound semiconductor nanowires are a promising solution for nanoscale optoelectronic devices such as lasers, LEDs, solar cells and photodetectors because of their high aspect ratio, large surface-to-volume ratio and carrier/photon confinement in two dimensions. In this work, we investigate the use of transparent conducting oxides (TCOs) to make a radial heterojunction InP nanowire array....

Nanowires have been studied extensively in the last decades because they promise substantial improvements in several technologies. Ordered arrays of nanowires can generate similar photocurrent densities as thin-film solar cells by using only a fraction of the material. Due to their high aspect ratio nanowires are very surface sensitive, which can be challenging for (opto-)electronics. For...

Semiconductor nanowires are routinely grown on high-priced crystalline substrates as it is extremely challenging to grow directly on plastics and flexible substrates due to high temperature requirements and substrate preparation. At the same time, plastic substrates can offer many advantages such as extremely low price, light weight, mechanical flexibility, shock and thermal resistance, and...

Thermoelectric properties of semiconductors – the ideal materials for thermoelectrics due to their advantageous electro/thermal transport properties – are rather fixed in standard devices, and little to no room is available for modulation of parameters influencing the thermoelectric figure of merit ZT=σS^2 T/κ, where σ is the electrical conductivity, S is the Seebeck coefficient, κ is the...

Research interest in indium antimonide (InSb) has increased in recent years thanks
to the possibility to overcome the limitation of its integration with lattice-mismatched materials in nano-heterostructures and consequent opportunities to realize novel quantum devices. Hence, precise control over morphology and crystalline quality becomes of paramount importance. Here, we show growth of InSb...

Charge carrier mobility and concentration are fundamental quantities related to the electrical properties of semiconductors, which severely affect their performance in electronic devices for fundamental studies as well as commercial applications. These two quantities can be affected by numerous physical and chemical sources; among these, doping is one of the most relevant, being at the same...

Novel transistor concepts based on semiconductor nanowires promise high performance, lower energy consumption and better integrability in various platforms in nanoscale dimensions. Concerning the intrinsic transport properties of electrons in nanowires, relatively high mobility values that approach those in bulk crystals have been obtained only in core/shell heterostructures, where electrons...

Semiconductor nanowires (NW) have received much attention for their unique properties providing exceptional flexibility in device engineering. In particular, gallium phosphide NWs demonstrate effective wave-guiding properties and broadband nonlinear frequency conversion, and find applications in green to amber optical range optoelectronics and photocatalytic devices.

NW elastic strain...

The search of Si-compatible light emitting material, has been a big challenge to science for several decades. Recently we have shown light emission from silicon [1]. In the hexagonal phase hex-Ge is a direct semiconductor, as the L-point is folded onto the Γ-point [2]. For the theoretical band energies of Hex-Si$_{1-x}$Ge$_{x}$ alloy, it is predicted that the Hex-SiGe compositions have a...

The Hex-Si$_{1-x}$Ge$_x$ nanowire material system provides a new direct bandgap semiconductor which is compatible with silicon opto-electronics[1]. Due to the change in crystal structure from cubic to hexagonal, a direct bandgap emerges as the L-point is folded towards the Γ-point[2]. For hex-Ge however, theoretical calculations predict a long 20µs radiative lifetime [1]. For efficient light...

Information and communication technology has become ubiquitous in everyday life. Emerging distributed computing paradigms such as the Internet of Things are demanding the implementation of novel electronic device functionalities that go beyond the capabilities of conventional field effect transistors. In this context, nanometer scale Ge departs from its bulk counterpart and delivers unique...

We present a combined experimental and theoretical effort to fabricate NiSi$_2$-Si interfaces in nanowire structures and to understand the resulting Schottky barrier height, which is essential for the subsequent transport properties.
The NiSi$_2$-Si interfaces were created using silicidation of top-down fabricated silicon nanowires. Silicidation was performed using either rapid thermal or...

Heterostructures made of single III-V semiconductor nanowires and an in-situ grown superconductor have led to some of the best quality -but still debated- signatures of Majorana end modes in solid state devices. More robust evidence of these modes, such as the topological Kondo effect, parafermions, and Majorana box qubits, is theorized to lie in pairs of nanowires in contact to a...

Conventional transistor topologies are limited to static electrical functions and demand extraordinarily steep and reproducible doping concentration gradients at the junctions. Reaching the physical limits of scaling, doping-free reconfigurable field-effect transistors (RFETs), capable of integrating logic functions in a complementary design by dynamically altering the device either to p- or...

Over the past few decades, the field effect transistors (FET) scaling followed mainly Moore’s law. However, with the downscaling of FET reaching its physical limitations, the quest for alternate technological solutions based on new device materials and concepts is on the rise. In this era of “Beyond CMOS”, various new researches and technologies have emerged, which focus on diversifying the...

Single silicon nanowire (SiNW) omega-gate Field Effect Transistors (FETs) and resistors have been fabricated using the standard photolithography method on a Kapton flexible polyamide thin film attached to a sacrificial Silicon substrate. SiNWs have been grown by chemical vapor deposition (CVD) method using Vapour-Liquid-Solid (VLS) mechanism and gold as a catalyst. We developed a robust...

Few years ago we demonstrated the use of site-selective synthesis of nanowires on top micromembranes as an energy-efficient and low cost methodology for their integration [1]. For this, micromembranes, which contained surface interdigitate microelectrodes and buried heaters, when the latter were biased, promoted the decomposition of the chemical precursor and the growth of the nanowires. In...

Microcantilevers are already successfully implemented in mass sensing devices, offering a sensitivity down to the range of few picograms. While for mass sensing applications the frequency shift is used, the corresponding quality factor additionally depends on the ambient medium and scales inversely with the pressure. However, the sensing range of commercial microcantilevers is restricted,...

Silicon nanowires (Si NWs) have been identified as an excellent candidate material for replacement of graphite in anodes, allowing for a significant boost in the capacity and cycle-life of LIBs. The growth of these NWs on low surface area planar substrates has limited the ability to achieve high loading and mechanical robustness. Here, we demonstrate the grow of high-density Si NWs on a novel...

Sodium-ion batteries development has gained momentum due to the high abundance of its raw material in the earth's crust, combined with their low cost as compared to resources required for Li-ion batteries. However, due to the large ionic radius of Na as compared to Li, the former intercalation in some of the well-developed Li-ion anode materials (e.g. Si, Ge, graphite) becomes difficult. The...

The controlled alignment and assembly of single, bottom-up grown nanowires on a target device substrate is an omnipresent challenge but indispensable for a reproducible fabrication of nanoscale electronic devices. Among various transfer techniques, nanowire contact printing (CP) due to mechanical shearing of the nanowire growth and the prospective device substrate enables immediate parallel...

Quasi 1D nanostructures exhibit outstanding properties, making them highly interesting for integration in optical, magnetic, electronic, thermal or multifunctional applications. Especially the latter, however, has very high demands on related fabrication as it not only requires local precision but also should allow the fabrication of different materials and / or the localized modification to...

The bottom-up synthesis of silicon nanowires (SiNWs) has traditionally been associated with challenging reaction conditions such as high temperatures, sub-atmospheric pressures and long reaction times. In this work, we have developed a bottom-up synthesis method for SiNWs at temperatures as low as 380 °C, using atmospheric pressures and reaction times as short as 60 seconds. These favourable...

Silicon nanostructures have outstanding and tunable optoelectronic properties. Three-dimensional control over their geometry is expected to lead to significant advances in a variety of fields. To date, this has been a challenging task.
Our group has become expert in synthesizing silicon nanowire arrays with controlled geometries via metal-assisted chemical etching (MACE). Our recent advances...

Due to its piezoelectric properties, zinc oxide (ZnO) is a promising candidate as a sensor material for condition monitoring and in haptic sensors, especially in the form of nanowires (NWs).

Although there are many ways to synthesize ZnO-NWs, such as the hydrothermal growth, the plasma flight-thru process offers several advantages, namely short process times, high throughput and...

All inorganic perovskite CsPbBr3 nanowires (NWs) have shown excellent performance in various optoelectronic applications such as laser, LED, and photodetection. There have been many studies reported for the growth of CsPbBr3 NWs arrays. However, there NWs are horizontal and cannot be used for devices requiring vertical photon or electron transportation. So far, studies on vertically aligned...

Inhomogeneity in the structural and material quality of semiconductor nanowires (NWs) can lead to variation in the optical properties and functional performance. While often a challenge, this variation can provide insights into energy dynamics by characterising many NWs and identifying correlations between parameters [1]. In this work we study CsPbBr3 perovskites NWs grown epitaxially on c-...

Following the discovery of carbon nanotubes by Iijima, there has been great interest in the synthesis and characterization of other one-dimensional (1D) structures, which include nanowires, nanorods and nanobelts constituting promising building blocks for many existing and emerging applications. Different synthetic strategies have been proposed while scaffold assisted bottom-up growth...

Organic semiconductor crystals are often characterized by a strong anisotropy in their electrical and optical properties. In addition, vapor deposition of rod-like molecules often yield epitaxially grown crystallites with extreme length to width ratio. These kinds of wires are interesting candidates for functional components in organic electronics. Especially the conjunction of organic...

Si-based multiwavelength light sources are of great interest for applications in photonics and multiplexed signal communication. The realization of an innovative hybrid light source operating at room temperature, obtained by embedding a carbon nanotube (CNT) dispersion inside a Si nanowire (NW) array is reported. Ultrathin Si nanowires (NWs) synthesized by metal-assisted chemical wet etching...