The structure and optical properties of silicon nanowires prepared by inductively coupled plasma chemical vapor deposition
Introduction
Silicon nanowires (SiNWs) have attracted more and more attention because of their promising applications in various nanowire-based photovoltaic (PV) solar cell structures [1], [2], [3], [4]. They have been utilized as ideal light trapping/absorbing materials [2], [5], [6], conductive paths for collecting photo-generated carriers [7] or nanoscaled frames for single silicon nanowire solar cells [8].
To date, different methods have been used to grow SiNWs, such as chemical vapor deposition (CVD) [9], laser-ablation [10], evaporation [11], solution-based methods [12] and so on. Among those, plasma enhanced CVD can serve as one of the most promising method because it can be used in a large area production and prepare both intrinsic and n- or p-doped semiconducting nanostructures. The low-power plasma significantly increases the growth rate at a low substrate temperature [13], [14], [15], [16]. Furthermore, a low-temperature growth process of silicon nanostructures on glass or other transparent substrates is especially interesting for solar cell applications [2], [17].
In this paper, SiNWs were prepared, for the first time, by inductively coupled plasma CVD. The impact of power and catalyst size on the structure and optical properties of SiNWs was explored.
Section snippets
Experimental details
P-type Si (111) wafers were employed as substrates. The substrates were ultrasonically cleaned in an acetone and ethanol solution in turns for 10 min, and then immersed in 5% HF solution for 5 min to remove the native oxide. Two kinds of Au colloids with nanoparticle size of 16 nm and 40 nm which were obtained by the reduction of aqueous HAuCl4 solution by sodium citrate at 100 °C, were used as catalyst for SiNWs growth. The substrate coated with Au colloids was pretreated by H2 plasma (400 W RF
Results and discussion
Fig. 1 shows the TEM images of SiNWs grown at 50 W with a catalyst size of 16 nm. A spherical Au nanoparticle at the tip of the silicon nanowire can be observed in Fig. 1(a), which is typical for the VLS mechanism. The tip is high crystalline with visible Si (111) lattice fringes separated by a spacing of 0.31 nm, and has a growth direction along < 110>. The TEM images of the root of a silicon nanowire (about 100 nm thick) located several micrometers below the tip are shown in Fig. 1(b). The central
Conclusions
The crystalline-amorphous core-shell SiNWs were prepared by ICP-CVD for the first time, which provides a chance to fabricate radial a-Si/crystalline silicon heterojunction solar cell. We found that the use of plasma was necessary for the growth of SiNWs from Au catalyst at a temperature as low as 380 °C. The dense and long SiNWs with thick amorphous shell were obtained by an increase in the plasma power. Small catalyst nanoparticles are easier activated by plasma to grow the dense and thin
Acknowledgements
This work was supported by the National Natural Science Foundation of China (No. 60776009) and the Natural Science Foundation of Gansu Province (No. 096RJZA056).
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