Search

Selective area growth (SAG) of GaN nanowires was performed on GaN on c-plane sapphire templates masked with SiN using hydride vapor phase epitaxy (HVPE). GaN nanowires exhibited various morphologies, discussed as a function of the pattern design, the partial pressure of the Ga gaseous precursor, the composition of the carrier gas, and the growth temperature. The morphologies are elucidated by involving a comparative study of growth rates of facets relative to each other. CL measurements showed high emission quality for GaN nanowires grown at 930 °C. This work places HVPE as an effective epitaxial technique for growing III–N nanostructure-based devices at a low cost.

We report on the selective area growth (SAG) of GaAs nanowires (NWs) by the catalyst-free vapor-solid mechanism. Well-ordered GaAs NWs were grown on GaAs(111)B substrates patterned with a dielectric mask using hydride vapor phase epitaxy (HVPE). GaAs NWs were grown along the ⟨111⟩B direction with perfect hexagonal shape when the hole’s opening diameter in SiNxor SiOxmask was varied from 80 to 340 nm. The impact of growth conditions and the hole size on the NW lengths and growth rates was investigated. A saturation of the NW lengths was observed at high partial pressures of As4, explained by the presence of As trimers on the (111)B surface at the NW top surface. By decreasing As4partial pressure and decreasing the hole size, high aspect ratio NWs were obtained. The longest and thinnest NWs grew faster than a two-dimensional layer under the same conditions, which strongly suggests that surface diffusion of Ga adatoms from the NW sidewalls to their top contributes to the resulting axial growth rate. These findings were supported by a dedicated model. The study highlights the capability of the HVPE process to grow high aspect ratio GaAs NW arrays with high selectivity.

In this work, we demonstrate the growth of vertically oriented GaAs nanowires (NWs) and microplatelets directly on a patterned SiO2/Si(111) substrate by hydride vapor-phase epitaxy (HVPE). Direct condensation of GaAs on Si was achieved through a critical surface preparation under an As-controlled atmosphere. GaAs NWs were grown along the ⟨111⟩Bdirection with a hexagonal cross section when the hole opening diameter (D) in the SiO2mask was below 350 nm. Larger apertures (D≥ 500 nm) resulted in uniform microplatelets. This study highlights the capability of HVPE for selective area growth of GaAs directly on Si and thus the potential of HVPE as a generic heterointegration process for III–V semiconductors on silicon.

We report on the selective area growth of InAs nanowires (NWs) by the catalyst-free vapor–solid method. Well-ordered InAs NWs were grown on GaAs(111)B and Si(111) substrates patterned with a dielectric mask using hydride vapor phase epitaxy (HVPE). Vertical and high aspect ratio InAs NWs with a hexagonal shape were grown on both GaAs and Si substrates. The impact of the growth conditions on the InAs morphology was investigated. The final shape of the InAs crystal was tuned from a NW to a nanoplatelet by controlling growth conditions such as growth temperature, vapor phase composition, and mask pattern. The influence of the aperture size on the nucleation density and then on the morphology of InAs is discussed. Small openings resulted in the formation of a single nucleus per hole, which was then converted to a NW. For larger apertures, the number of nuclei increased, leading to both three-dimensional crystals and NWs. The effect of growth temperature and the III/V ratio on the kinetics and thermodynamics of InAs growth is also discussed. The growth was first optimized on a GaAs(111)B substrate and then performed on Si, which is more suitable to develop devices. Finally, the absorbance and photoluminescence measurements were carried out on the InAs NW arrays, demonstrating the high potential of HVPE-grown InAs NWs for future multispectral photo-detection devices.

Au droplets are used as a catalyst for the growth of nanowires on Si(111) substrate via the vapor–liquid–solid (VLS) mechanism. The dewetting of a Au thin film is the most common method to obtain these droplets. The control of this step is crucial to adjust the density and the diameter of the nanowires during VLS growth. When the Si(111) substrate is covered with a silicon dioxide layer, the kinetics of Au droplet formation is strongly modified. The dependence of the diameter and spatial distribution of the droplets on the surface have been studied by scanning electron microscopy with respect to the thickness of the silicon dioxide layer, the thickness of the Au film and the temperature of the substrate during deposition and postdeposition annealing. In situlow energy electron microscopy and low energy electron diffraction revealed the dynamics of the Au droplet formation after annealing. The Au droplets are shown to catalyze the decomposition of silicon dioxide at high temperature (>650–700 °C) and form a wetting layer of Au-(√3×√3)-Si(111). Consequently, the droplets absorb silicon atoms from the substrate, migrate perpendicular to the atomic steps, and grow by the Smoluchowski ripening process.

Control over the morphology of InN nanorods, which remains challenging due to the complex mechanisms involved in the growth process, is essential for the next generation of nano- and optoelectronic devices. In this paper, we report on the selective area growth (SAG) of InN nanorods on Ga-polar GaN/c-Al2O3templates using hydride vapor-phase epitaxy (HVPE). A systematic study of the evolution of the shape of InN nanorods under various growth conditions—growth temperature, growth time, and the input NH3partial pressure—is carried out. The optimal growth temperature to achieve a perfect selectivity and prevent InN decomposition is first determined. The dependence of the axial and radial growth rates on the growth temperature and vapor phase composition with group V elements is discussed. The influence of mass transport on the InN nanorods’ geometry is shown to be more pronounced at extended growth times. Swapping of the nanorods’ morphology from pencil to a perfect hexagonal shape is controlled by varying the growth time. Photoluminescence measurements on InN nanorods are interpreted by considering a concentration of free electrons. The results reported herein provide relevant information for understanding SAG of InN and could pave the way to develop high-performance InN nanorods-based devices.

The incorporation of Si into vapor–liquid–solid GaAs nanowires often leads to p-type doping, whereas it is routinely used as an n-dopant of planar layers. This property limits the applications of GaAs nanowires in electronic and optoelectronic devices. The strong amphoteric behavior of Si in nanowires is not yet fully understood. Here, we present the first attempt to quantify this behavior as a function of the droplet composition and temperature. It is shown that the doping type critically depends on the As/Ga ratio in the droplet. In sharp contrast to vapor–solid growth, the droplet contains very few As atoms, which enhance their reverse transfer from solid to liquid. As a result, Si atoms preferentially replace As in GaAs, leading to p-type doping in nanowires. Hydride vapor phase epitaxy provides the highest As concentrations in the catalyst droplets during their vapor–liquid–solid growth, resulting in n-type dopant behavior of Si. We present experimental data on n-doped Si-doped GaAs nanowires grown by this method and explain the doping within our model. These results give a clear route for obtaining n-type or p-type Si doping in GaAs nanowires and may be extended to other III–V nanowires.

Despite the unavoidable presence of silicon atoms in the catalyst alloy droplets during the vapor–liquid–solid growth of III–V nanowires on silicon substrates, it remains unknown how the nucleation of nanowires is affected by these foreign atoms. In this work, we present the first attempt to quantify the nanowire nucleation rate versus the silicon concentration in the droplet. We calculate the chemical potential difference per Ga–As pair in the quaternary Au–Ga–As–Si liquid alloy droplet and in solid state, and compare it to the ternary Au–Ga–As droplet without silicon. This allows us to compute the nucleation rates of GaAs nanowires versus the silicon concentration under different conditions. We find that the presence of silicon in the droplet decreases the nucleation probability of GaAs nanowires for gallium-rich droplets (with the gallium contents cGAgreater than 0.6) and increases it for gold-rich droplets (cGA< 0.6). The model is used to explain our experimental data for hydride vapor phase epitaxy of gold-catalyzed GaAs nanowires, which easily nucleate on Si(111) covered with different SiO2layers but do not grow on the bare Si(111). In the latter case, more silicon is etched from the substrate and enters the gallium-rich droplets, which suppresses the nanowire nucleation. We discuss other relevant data, including the known difficulties in obtaining self-assisted GaAs NWs on silicon by chemical epitaxy techniques. These results may be useful for the fine-tuning of III–V nanowire properties and integrating them with silicon electronics.