Competition between uncatalyzed and catalyzed growth during the plasma synthesis of Si nanowires and its role on their optical properties

Abstract

In this paper, we study the metal-catalyzed synthesis of Si nanowires (Si-NWs) in a plasma based chemical vapor deposition system. In these deposition systems due to the high efficiency of precursor molecule dissociation, both uncatalyzed and catalyzed growth mechanisms can take place. The first one gives rise to the formation of the quasi one-dimensional (1D) Si-NWs, while the second one to a continuous two-dimensional (2D) Si layer over the substrate or on the nucleated Si-NWs. The Si-NWs formation is then the result of the competition between these two processes. The control parameters ruling these two contributions are here explored. Samples with different weights of 1D and 2D growth are deposited and characterized by using a plasma based chemical vapor deposition apparatus operating at T < 400 °C. It is found that the main control parameter of these processes is the plasma power through the distribution of the precursor dissociation products. By properly tuning the power, Si-NWs with 1 × 1010 cm−2 of density, up to 1 μm long and without uncatalyzed growth are obtained. The optical functionality of the samples, grown with different 1D/2D contributions, is investigated and it is demonstrated that the uncatalyzed layer produces a total reflectance as high as ∼40%, similar to that found in a planar Si wafer, while the highly dense Si-NWs, without the uncatalyzed deposition, produce a total reflectance of ∼15%.

Silicon Quasi‐One‐Dimensional Nanostructures for Photovoltaic Applications

“…Moreover, in an inductively coupled plasma (ICP) CVD reactor, the high plasma density and the absence of acceleration of ions toward the substrate grant the absence of structural substrate damage. In reference [17], different plasma power values between 0 and 1000 W were explored to study its role on the Si NWs growth. Morphological results showed that three growth regimes can be identified: a low plasma region from 0 to 60 W, where only 1D SiNW structures were grown, an intermediate region from 60 to 100 W where both 1D and 2D films were obtained, and a third zone at high plasma power (from 100 to 1000 W) where SiNWs were absent and only continuous uncatalyzed Si layer was obtained.…”

“…Many aspects dramatically controlling the NW morphology like the precursor flow gas [14], the substrate type, and crystallographic orientation [8,12,15]; the SiNWs growth direction [12] and substrate surface chemical conditions [16] will be reviewed and discussed. When SiNWs are deposited by using plasma enhanced chemical vapor deposition (CVD) systems, also the plasma power plays an important role in the formation of SiNWs [17]. The most common metal exploited as a catalyst is gold, thanks to its low eutectic temperature.…”

Silicon nanowires to detect electric signals from living cells

“…PECVD indeed proved successful for NW growth at a relatively fast rate often below the eutectic point of the different catalysts used (e.g., Au [14][15][16]; Al [17]; Ga or In [16][17][18]). However, PECVD leads to the formation of mixed amorphous/crystalline structures, making the separation of the deposition by-products from NWs difficult [19]. A crucial point in this field is thus the ability to keep separated the nano-structure and the crystalline form of the deposited material, while working at relatively low-temperature.…”

Influence of hydrofluoric acid treatment on electroless deposition of Au clusters

“…Gold nanoparticles on silicon substrates have shown quite interesting applications in the fields of Si nanowire (SiNW) catalysis [ 1 – 3 ], metal-assisted etching (MAE) [ 4 ] or even as electrical contacts in standard miniaturized devices [ 5 ]. Their ability to display enhanced surface plasmon resonance (SPR) at optical frequencies makes them excellent at scattering and absorbing visible light [ 6 – 8 ].…”