Light-emitting silicon nanowires obtained by metal-assisted chemical etching

Abstract

This review reports on a new process for the synthesis of Si nanowires (NWs), based on the wet etching of Si substrates assisted by a thin metal film. The approach exploits the thicknessdependent morphology of the metal layers to define uncovered nanometric Si regions, which behave as precursor sites for the formation of very dense (up to 1×10 12 NW cm −2 ) arrays of long (up to several μm) and ultrathin (diameter of 5-9 nm) NWs. Intense photoluminescence (PL) peaks, characterized by maxima in the 640-750 nm range and by an external quantum efficiency of 0.5%, are observed when the Si NWs are excited at room temperature. The spectra show a blueshift if the size of the NW is decreased, in agreement with the occurrence of quantum confinement effects. The same etching process can be used to obtain ultrathin Si/Ge NWs from a Si/Ge multi-quantum well. The Si/Ge NWs exhibit-in addition to the Si-related PL peak-a signal at about 1240 nm due to Ge nanostructures. The huge surface area of the Si NW arrays can be exploited for sensing and analytical applications. The dependence of the PL intensity on the chemical composition of the surface indeed suggests interesting perspectives for the detection of gaseous molecules. Moreover, Si NWs decorated with Ag nanoparticles can be effectively employed in the interference-free laser desorption-ionization mass spectrometry of lowmolecular-weight analytes. A device based on conductive Si NWs, showing intense and stable electroluminescence at an excitation voltage as low as 2 V, is also presented. The unique features of the proposed synthesis (the process is cheap, fast, maskless and compatible with Si technology) and the unusual optical properties of the material open the route towards new and unexpected perspectives for semiconductor NWs in photonics.

Effect of annealing temperature on thermo‐diffusional boron doping of silicon nanowire arrays probed by Raman spectroscopy

“…[ 32,33,35,36 ] Note that in this case, the observed distortions in Raman spectra correspond to theoretical considerations that phonon confinement reveals itself in the structures with a diameter less that 10–20 nm. [ 23–29,31–34 ] We do not observe any maximum red shift within the chosen spectral resolution or a broader half‐width at the lower wavenumber side of the Raman spectra of as‐prepared and thermally annealed SiNWs (Figure 2a) as could be expected for small‐diameter nanowires. [ 31 ] We also have a good fit by the Fano‐resonance model (Equation ) as shown in Figure 3 and Figure 5.…”

“…Because the Raman line shape can be modified by phonon confinement, [ 22–36 ] one should be scrupulous about the possible impact of phonon confinement to the estimations of the FCC concentration in SiNWs. MACE formation of SiNW arrays on highly boron‐doped c‐Si substrates leads to the narrowing of nanowire diameter and additional nanowire porosity that results in a distortion of the lower wavenumber side of Fano‐resonance line.…”

Probing two-level systems with electron spin inversion recovery of defects at the Si/SiO2 interface

“…For both samples, any residual metal impurities are expected to remain close to the tips of the nanowires, therefore, affecting less than 0.2% of the DBs that we probe experimentally. The metal contamination in SiNWs produced by MACE, in contrast with those produced by the vaporliquid-solid method with a metal catalyst, has been found negligible by different experimental methods [21][22][23][24]. The full process led to a dense carpet of straight silicon nanowires, fully passivated with H and with structural parameters dependent on the process details ( Fig.…”

Catalytic Activity of Silicon Nanowires Decorated with Gold and Copper Nanoparticles Deposited by Pulsed Laser Ablation

“…Among them, the chemical etching approach proved to be a more rapid and practical technique for producing uniform SiNWs at room temperature with inexpensive and scalable procedures [15,16,17]. …”