Elucidating the Effect of Etching Time Key-Parameter toward Optically and Electrically-Active Silicon Nanowires

Abstract

In this work, vertically aligned silicon nanowires (SiNWs) with relatively high crystallinity have been fabricated through a facile, reliable, and cost-effective metal assisted chemical etching method. After introducing an itemized elucidation of the fabrication process, the effect of varying etching time on morphological, structural, optical, and electrical properties of SiNWs was analysed. The NWs length increased with increasing etching time, whereas the wires filling ratio decreased. The broadband photoluminescence (PL) emission was originated from self-generated silicon nanocrystallites (SiNCs) and their size were derived through an analytical model. FTIR spectroscopy confirms that the PL deterioration for extended time is owing to the restriction of excitation volume and therefore reduction of effective light-emitting crystallites. These SiNWs are very effective in reducing the reflectance to 9-15% in comparison with Si wafer. I-V characteristics revealed that the rectifying behaviour and the diode parameters calculated from conventional thermionic emission and Cheung's model depend on the geometry of SiNWs. We deduce that judicious control of etching time or otherwise SiNWs' length is the key to ensure better optical and electrical properties of SiNWs. Our findings demonstrate that shorter SiNWs are much more optically and electrically active which is auspicious for the use in optoelectronic devices and solar cells applications.Nanomaterials 2020, 10, 404 2 of 18 time-consuming and therefore hindered their applications for commercialized products. In contrast, an effective and promising synthetic method namely metal assisted chemical etching (MACE) has been proposed [2,4,[18][19][20]. This technique is simple, rapid, low cost, and suitable for both industrial and laboratory scales. Moreover, MACE allows to obtain high crystalline SiNWs quality, as well as an easy control of the different parameters including orientation, doping type, length, and diameter.The MACE method basically consists of two procedures, the formation of metal catalysts and the subsequent etching process which can be implemented either in a single step (1-MACE) [10,21] or in two steps (2-MACE) [17-20]. Moreover, the formation method, etching time, etching temperature, metal deposition time, and lastly the etchants' concentrations have a crucial influence on the morphology of SiNWs [2,5,17]. Ghosh et al. reported that SiNWs grown by MACE are usually covered with silicon nanocrystals due to the side wall etching and which are the origin of quantum confinement (QC) effects owing to their small dimensions [20]. Recently, several research groups have succeeded in the synthesis of optically-active SiNWs exhibiting a significant PL emission and a very low reflectance [3,4,17]. On the other hand, Qi et al. have demonstrated the fabrication of electrically-active SiNWs through heavily doped SiNWs with rough surface where a high Schottky barrier exists at the interface of SiNWs and the metal [22]. Nevertheless, further investigation is required t...

Highly Efficient Silicon Nanowire Surface Passivation by Bismuth Nano-Coating for Multifunctional Bi@SiNWs Heterostructures

“…SiNW arrays were synthesized via a two-step Ag-assisted chemical etching method. An itemized explanation of the fabrication mechanism and the chemical reactions that occurred during the etching process are reported in our previous work [ 8 ]. Figure 2 a depicts a typical top-view SEM image of the as-prepared SiNWs.…”

“…Finally, the as-formed homogeneous black SiNWs were washed again with DI and dried with nitrogen. The SiNW fabrication mechanism is explained in our previous report [ 8 ].…”

“…Over the past few years, silicon nanowires (SiNWs) have aroused colossal attention worldwide both at the academic and technological level owing to the following fascinating peculiarities: (1) silicon is the second most earth-abundant material after oxygen, non-toxic, and environmentally friendly; (2) SiNWs have a distinct one-dimensional “1D” structure; (3) they have unique optical and electrical properties compared to bare silicon; (4) they have potential applications in several fields, ranging from solar cells, catalysis, and electronics to sensors [ 1 , 2 , 3 , 4 , 5 ]; and (5) they have affordable fabrication via numerous methods, including chemical vapor deposition (CVD), lithography, molecular beam epitaxy, laser ablation, and metal-assisted chemical etching (MACE) [ 3 , 4 , 5 , 6 , 7 , 8 , 9 ]. Among these methods, MACE is particularly intriguing and promising because of its simplicity, good cost-efficiency, and reliability [ 7 , 8 ]. It essentially consists of two processes—the formation of metal catalysts on the surface of Si substrates, and the subsequent etching leading to SiNWs formation—which can be implemented either in a single step (1-MACE) [ 3 ] or in two steps (2-MACE) [ 7 , 8 , 9 ].…”

“…Among these methods, MACE is particularly intriguing and promising because of its simplicity, good cost-efficiency, and reliability [ 7 , 8 ]. It essentially consists of two processes—the formation of metal catalysts on the surface of Si substrates, and the subsequent etching leading to SiNWs formation—which can be implemented either in a single step (1-MACE) [ 3 ] or in two steps (2-MACE) [ 7 , 8 , 9 ]. Commonly, the MACE-grown SiNW arrays are covered with porous structures—namely, silicon nanocrystals (SiNCs)—resulting from the lateral etching of NW side walls [ 7 , 8 , 9 ].…”

“…It essentially consists of two processes—the formation of metal catalysts on the surface of Si substrates, and the subsequent etching leading to SiNWs formation—which can be implemented either in a single step (1-MACE) [ 3 ] or in two steps (2-MACE) [ 7 , 8 , 9 ]. Commonly, the MACE-grown SiNW arrays are covered with porous structures—namely, silicon nanocrystals (SiNCs)—resulting from the lateral etching of NW side walls [ 7 , 8 , 9 ]. Therefore, porous SiNWs are a promising host matrix to load and disperse a diverse set of functionalities and complexities according to the requirements.…”