Porosity Control for Plasma-Assisted Molecular Beam Epitaxy of GaN Nanowires

Abstract

We report on the bottom-up fabrication, by plasma-assisted molecular beam epitaxy, of monocrystalline GaN solid, hollow, and c-shape nanowires deposited in a compact fashion. The shape exhibited by these nanostructures varies from solid to c-shape and hollow nanowires. They were epitaxially grown with their [0001] directions perpendicular with respect to different surfaces of Si substrates. Advanced studies of these GaN nanostructures were carried out by means of selected-area electron diffraction and scanning and high-resolution transmission electron microscopy evidencing their structure and epitaxial alignments with respect to the silicon. Through a comprehensive analysis of the growth conditions (substrate temperature and Ga and N* fluxes) we demonstrate that a local Ga-limited regime is the mechanism behind the particular shape of these nanostructures. Additionally, spectroscopic ellipsometry studies, applying a model based on Bruggeman effective medium approximations and taking into account several aspects related to the nature of these GaN nanostructures, were carried out to obtain valuable information about the evolution of the optical constants and the porosity along the layer. This work shows a way to control the porosity and shape of GaN nanowires by varying the growth conditions, which could open new horizons in the development of GaN nanostructures for future applications.

Simultaneous Optical and Electrical Characterization of GaN Nanowire Arrays by Means of Vis-IR Spectroscopic Ellipsometry

“…Wurtzite GaN nanowire layers were grown on chemically cleaned p-type Si(111) or (100) substrates by PAMBE along the [0001] direction, and epitaxially aligned with the underlying Si substrate, following the same procedure as the one described in a previous study 10 . For 3D reconstructions, two different systems were used to acquire FIB-SEM tomography datasets: a Scios 2 DualBeam microscope from Thermo Scientific and a CrossBeam 350 microscope from ZEISS.…”

“…By tuning the growth conditions, the size and arrangement of the nanowires, and thus the porosity, can be controlled so as to modulate the optical and electrical properties of the system 5,[8][9][10][11] . Thanks to its high surface-to-volume ratio, tuneable refractive index and bandgap, high light extraction efficiency and quantum efficiency, GaN arrays have been erected as a promising material not only for the development of optoelectronic and optical devices such as field-effect transistors (FETs) 12,13 , light-emitting diodes (LEDs) 6,14 , laser diodes 15 and detectors 16 , but also for photoelectrochemical water splitting 17,18 and energy storage 19 applications.…”

“…While the optical characterization of GaN nanowire and nanorod arrays through spectroscopic ellipsometry (SE) 9,10 , polarized-goniometry 20 or reflectivity spectroscopy 11 is well reported in the literature, the characterization of electrical properties related to conductivity, like carrier concentration and mobility, presents some difficulties associated to the geometry of this kind of structures 4,21 . Up to now, the majority of the studies are focused on Hall effect and field effect measurements performed on single nanowires after fabricating multiple contacts [22][23][24][25] .…”

A comparative study of micro- and nano-structured di-nuclear Co(II) complex, designed to produce efficient nano-sorbent of Co3O4 applicable in the removal of Pb2+

“…This confirms that the structure of complex 1 which synthesized by the hydrothermal method is the same to that synthesized by the sonochemical process. All three patterns contain diffraction peaks at 2θ = 6.5°, 9.8°, 11 [42]. Figure 5, shows the FT-IR spectra of hc and uc complexes.…”

“…In another study, Khalaji et al [5] prepared Co 3 O 4 nanoparticles with an average particles size in the range of 10-20 nm by thermal decomposition of a cobalt(III) Schiff base complex. Many methods have been attempted to prepare transition metal oxide nanoscale such as chemical vapor deposition (CVD) [6], hydrothermal methods [7], microwave irradiation [8], electrochemical deposition [9], soft chemical solution [10] and molecular beam epitaxy [11]. Several methods have been reported for the removal of dye and toxic metal ions from the environment such as, cloud point extraction [12], ionexchange [13], flocculation-coagulation [14], solid-phase extraction [15], photocatalysis [16] and direct adsorption [17].…”