Metal-induced Etching Research Articles

The effect of dopant on light trapping characteristics in random silicon nanowires for solar cell applications

The Light management is a fundamental study to improve the solar cell and photoelectrical devices conversion efficiency. Here, the spectral responses of reflection and absorption characteristics of random silicon nanowires (Si-NWs) arrays of different lengths and doping type has been investigated. The Si-NWs have been synthesized by metal induced etching (MIE) approach have dimensions of Sub-wavelength regime. These Si-NWs arrays show efficient light trapping and low reflectance than bare Si due to suppression of Fresnel reflection substantially over a wide spectral range. The comparative study of light trapping in Si-NWs, fabrication by using n-type and p-type Si wafer have been explored to add new dimension in the field of photovoltaic application. Here, diffuse reflection spectra have been used to analyzed the light-scattering properties of Si-NWs, which reveal that the diffuse scattering decreases as the pore depth increases. The field distribution of Si-NWs is simulated using finite differential time domain (FDTD) method, results shows that reflectance could be modified due to light absorption driven by multiple scattering inside the structure reaching high values of apparent absorbance. Current-voltage (I–V) curves have been measured under illumination at standard testing conditions (STC), i.e., 300 K, 1000 W/m2 and 1.5 a.m. global by using solar simulator. These measurement studies indicate that dopant (n-type and p-type) have been effectively influenced the photovoltaic parameters. I–V curve indicated that the power conversion efficiency (PCE) of n-type and p-type doped Si-NWs exhibited PCE of 3.94% and 4.01% respectively.

Size dependence of Raman line-shape parameters due to confined phonons in silicon nanowires

ABSTRACT A comparison of experimentally observed Raman scattering data with Raman line shapes, generated theoretically using a phonon confinement model, has been carried out to understand the sensitivity of different Raman spectral parameters towards the quantum confinement effect. Size-dependent variations of full width at half maximum, Raman peak position and asymmetry ratio have been analysed to establish the sensitivity of their corresponding physical counterparts (phonon lifetime and dispersion) in confined systems. The comparison has been done in three different confinement regimes, namely weakly, moderately and strongly. Proper reasoning has been assigned for such a variation after validation of the theoretical analysis with the experimental observations. A moderately confined system was created by preparing 6-nm-sized silicon nanostructures using metal-induced etching. An asymmetrically broadened and red-shifted Raman line shape was observed, which established that all the parameters get affected in a moderately confined system. Sensitivity of a given Raman spectral parameter has been shown to be used as a tool to understand the role of external perturbations in a material.

Spatial delocalization of absorption and emission process in silicon nanowires

Dependence of optical properties of porous silicon nanowires on their size has been investigated here. Based on the experimental evidence, a new model to explain the process of absorption and photoluminescence in these Si nanowire samples has been proposed. Three different samples, with different nanowire diameters, have been prepared using metal-induced etching of silicon wafers. These wafers have different doping type and doping concentration which results in silicon nanowires of different diameters embedded with Si nanostructures of sizes around the Bohr's exciton radius. The absorption properties of these different types of Si nanostructures show a strong size dependence. However, the photoluminescence spectrum does not show any direct dependence on the size of the nanostructures, doping levels and type of silicon wafer used for fabrication of silicon nanostructures. It is also observed that the photoluminescence life time from these structures inversely depends on the size of the nanostructures whereas directly depends on the porosity, thus defects, in the samples. Based on these results it has been shown that the absorption of photons in these porous silicon nanowires happens in the silicon nanostructures embedded in the nanowires while the photoluminescence emission originates due to the surrounding porous SiOx.

Role of metal nanoparticles on porosification of silicon by metal induced etching (MIE)

Porosification of silicon (Si) by metal induced etching (MIE) process has been studied here to understand the etching mechanism. The etching mechanism has been discussed on the basis of electron transfer from Si to metal ion (Ag+) and metal to H2O2. Role of silver nanoparticles (AgNPs) in the etching process has been investigated by studying the effect of AgNPs coverage on surface porosity. A quantitative analysis of SEM images, done using Image J, shows a direct correlation between AgNPs coverage and surface porosity after the porosification. Density of Si nanowires (NWs) also varies as a function of AgNPs fractional coverage which reasserts the fact that AgNPs governs the porosification process during MIE. The Raman and PL spectrum show the presence of Si NSs in the samples.

Spectroscopic Investigation of well aligned Silicon Nano wires Fabricated by Metal Induced Etching

Well aligned Silicon nano-wires (SiNWs) were fabricated by metal induced etching (MIE). Scanning electron microscopy has been employed to study the surface morphology and cross sectional view for confirming the nano-wire like structures in our samples. Presence of electronic continuum and quantum confinement effect in the SiNWs- samples has been revealed from Raman and photoluminescence (PL) spectroscopy. Blue emission is achieved from SiNWs sample. Moreover, the effect of etching time on fabrication of SiNWs and associated PL spectra are studied here. We found with increasing etching time, pores are broader resulting in smaller size nano-wires. With further increasing in etching time, these NWs broke from the top, resulted in a blunt top surface leading to large size NWs. After a certain etching time, upper part of SiNWs is being broken, which is also reflected in PL spectra. Raman Spectroscopy shows the phonon confinement and is used to estimate the particle size. A detailed results and discussions have been presented here

Study of Porous Silicon Prepared Using Metal-Induced Etching (MIE): a Comparison with Laser-Induced Etching (LIE)

Porous silicon (p-Si), prepared by two routes (metal induced etching (MIE) and laser induced etching (LIE)) have been studied by comparing the observed surface morphologies using SEM. A uniformly distributed smaller (submicron sized) pores are formed when MIE technique is used because the pore formation is driven by uniformly distributed metal (silver in present case) nanoparticles, deposited prior to the porosification step. Whereas in p-Si, prepared by LIE technique, wider pores with some variation in pore size as compared to MIE technique is observed because a laser having gaussian profile of intensity is used for porosification. Uniformly distribute well-aligned Si nanowires are observed in samples prepared by MIE method as seen using cross-sectional SEM imaging. A single photoluminescence (PL) peak at 1.96 eV corresponding to red emission at room temperature is observed which reveals that the Si nanowires, present in p-Si prepared by MIE, show quantum confinement effect. The single PL peak confirms the presence of uniform sized nanowires in MIE samples. These vertically aligned Si nanowires can be used for field emission application.

Silicon nanowires prepared by metal induced etching (MIE): good field emitters

Efficient field emission from silicon nanowires prepared using metal induced etching.

Antireflective silicon surface with vertical-aligned silicon nanowires realized by simple wet chemical etching processes

Silicon antireflection is realized with vertical-aligned SiNWs by using improved metal-induced etching technique. The spectral responses of the transmission, reflection, and absorption characteristics for the SiNWs of different lengths are investigated. In order to realize short SiNWs to provide sufficiently low reflection, a post chemical etching process is developed to make the nanowires have a larger length fluctuation and/or tapered structure. The use of short SiNWs can allow a faster process time and avoid the sub-bandgap absorption that frequently occurs in long nanowires. Short SiNWs can also provide more compatible material structure and fabrication procedures than long ones can for applying to make optoelectronic devices. Taking the applications to solar cells as examples, the SiNWs fabricated by the proposed technique can provide 92% of solar weighted absorption with about 720 nm long wires because of the resultant effective graded index and enhanced multiple optical scattering from the random SiNW lengths and tapered wires after KOH etching.

Ordered silicon nanowire arrays via nanosphere lithography and metal-induced etching

Two-dimensional silica colloidal crystal template is used to create metal nanohole arrays on a silicon surface, which enables the controlled fabrication of aligned silicon nanowire (SiNW) arrays via metal catalytic etching. By varying the size of silica colloidal crystals, aligned arrays of SiNWs with desirable diameter and density could be obtained. The formation of ordered SiNW arrays is due to selective and anisotropic etching of silicon induced by the silver pattern. The orientation of SiNW arrays is influenced by silver movement in silicon, and the wire axes are primarily along the ⟨100⟩ direction.