Effect of rf power on the growth of silicon nanowires by hot-wire assisted plasma enhanced chemical vapor deposition (HW-PECVD) technique

doi:10.1016/j.tsf.2011.01.056

Thin Solid Films

Volume 519, Issue 15, 31 May 2011, Pages 4933-4939

https://doi.org/10.1016/j.tsf.2011.01.056 Get rights and content

Abstract

Silicon nanowires (SiNWs) were synthesized by simultaneous evaporation of Au and Si deposition using H₂ diluted SiH₄. The deposition techniques combined hot-wire (HW) and plasma enhanced chemical vapor deposition (PECVD). Au wires were placed on the filament and heated simultaneously with the activation of the rf plasma for the dissociation of SiH₄ and H₂ gases. Five set of samples were deposited on ITO-coated glass substrate at different rf power varied from 20 to 100 W in an interval of 20 W, keeping other deposition parameters constant. High yield of SiNWs with diameter ranging from 60 to 400 nm and length about 10 μm were grown at rf power of 80 W (power density ~ 1018 mW cm⁻²). Rf power of 100 W (power density ~ 1273 mW cm⁻²) suppressed the growth of these SiNWs. The growth mechanisms of SiNWs are tentatively proposed. The nanocrystalline structure of SiNWs is confirmed by Raman spectra and HRTEM measurement.

Introduction

Chemical vapor deposition (CVD) technique is widely used for the fabrication of silicon nanowires (SiNWs) due to its great potential to produce high yield and well aligned nanowires (NWs) [1], [2], [3]. However, the utilization of high temperature in the synthesis of SiNWs (~ 600 °C) has limited its implementation in industrial manufacturing. Low temperature growth of Au catalyzed SiNWs using PECVD has been reported [4], [5], [6]. The assistance of plasma as a discharging source of precursor gas reduces the deposition temperature to less than 400 °C and also enhances the growth rate of SiNWs in CVD. HWCVD is well known in silicon-based thin film deposition due to its advantages of low cost, high deposition rate, ease of handling and provide ion free deposition [7]. Silane (SiH₄) gas can be decomposed to SiH_x related free radicals species depending on the filament temperatures [8]. However, information on the growth of SiNWs using HWCVD technique is currently not much reported in literature as the high rate of decomposition of precursor gas using HWCVD is preferred for thin film deposition rather than SiNWs growth [9].

In this work, we introduce a new technique for the fabrication of SiNWs on indium tin oxide (ITO) coated glass using a simultaneous evaporation of Au and dissociation of SiH₄ diluted in hydrogen (H₂) gas using hot-wire assisted PECVD (HW-PECVD) technique. In low temperature CVD process, the radio frequency (rf) power density is a crucial parameter for the growth of SiNWs. Increase in rf power is expected to enhance the dissociation of SiH₄ gas into reactive species, but, high rf power might deactivate the catalytic effect [4]. Hence, optimization of the rf power for growth of SiNWs is very important. The effects of rf power on the growth process, surface morphology, chemical composition and structural properties of SiNWs are studied.

Section snippets

Experimental

Five sets of samples were prepared on ITO coated glass substrate with surface resistivity of 8–12 Ω/sq at different rf powers of 20, 40, 60, 80 and 100 W using a home-built HW-PECVD system. A schematic diagram of the HW-PECVD reactor is shown in Fig. 1. The reactor consisted of two parallel electrodes within a stainless steel chamber, operated at radio frequency of 13.56 MHz. The upper stainless steel electrode which was also the gas showerhead was coupled to the plasma generator via an impedance

Results and discussion

Fig. 2 shows the FESEM images of samples prepared on ITO coated glass at different rf power. The morphologies of as-synthesized SiNWs were significantly influenced by rf power. For sample prepared at rf power of 20 W, two types of NWs were observed on film. Winded wires with diameter of ~ 300 nm elongated to a length of ~ 5 μm from catalyst droplets of 500 to 1000 nm in diameter and spiral NWs with diameter of ~ 60 nm grew from smaller catalyst droplets were present throughout the surface of the film.

Conclusions

This work show that the SiNWs can be grown by using simultaneous evaporation of Au and dissociation of H₂ diluted SiH₄ by HW-PECVD technique. The In/Au catalytic and Au catalytic growth of SiNWs follow the VLS mechanism. The NWs were nanocrystalline in structure with Si nanocrystallites embedded in an amorphous Si matrix. Increase in rf power resulted in increase of the yield and diameter of the NWs. The growth of SiNWs was totally suppressed at rf power of 100 W due to deactivation of catalyst

Acknowledgement

This work was supported by the Ministry of Higher Education under Fundamental Research Grant Scheme (FRGS) of FP008/2008C, University Malaya Research Grant (UMRG) of RG061/09AFR and University of Malaya Postgraduate Research Fund (PPP) of PS310/2009B.

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Effect of rf power on the growth of silicon nanowires by hot-wire assisted plasma enhanced chemical vapor deposition (HW-PECVD) technique

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Conclusions

Acknowledgement

Surf. Coat. Tech.

Thin Solid Films

Thin Solid Films

J. Cryst. Growth

J. Ind. Eng. Chem.

Appl. Surf. Sci.

Thin Solid Films

Microelectron. Eng.

Thin Solid Films

Mater. Sci. Eng.

Mater. Sci. Eng. C

Nucl Instr. Meth. Phys. Res. B

Phys. E