Morphological, structural, and functional properties of vertically aligned carbon nanotubes deposited on porous silicon layers by ultrasonic spray pyrolysis

Abstract

In this work, we reported the fabrication of hybrid structures by growing the multi-walled carbon nanotubes (MWCNT) on porous silicon (PS) as a template. Aligned multi-walled carbon nanotubes have been successfully synthesized on PS by ultrasonic spray pyrolysis (USP) using a solution of Toluene/Ferrocene as the precursor, while electrochemical anodization method was used to fabricate the PS layers. Au contact was deposited as a metallic contact on the MWCNT layer in order to measure the electrical properties and to analyze the electrical effect of the incorporation of MWCNT on PS. The structural and morphological characteristics of the hybrid structures were investigated by using Field Emission Scanning Electron Microscope (FE-SEM) showing that MWCNT formed a thin film on the PS surface in the form of an aligned array and perpendicular fiber-like structures to the porous surface. High-Resolution Transmission Electron Microscopy (HRTEM) images confirmed the diameter of the CNT between 10 and 30 nm and typically consisted of 10–20 concentric shells of carbon sheets. Raman Microscopy showed three characteristic bands and a high graphitization extent, even it was possible to observe that the carbon structures passivated the PS layer. Consequently, the photoluminescence (PL) spectrum of PS layers significantly was modified by MWCNT. Finally, electrical measurements provided a practical approach to describe how the materials behave under specific conditions that can be used for different applications in electronics or optoelectronics such as diodes or photodetectors. Significant differences were found under darkness, and illumination conditions of current-voltage (I–V) curves implied their possible application in optoelectronics. Moreover, symmetrical rectifying and Ohmic behavior was observed, which rarely has been reported in the literature, even it was possible to fit a transport mechanism, and the capacitance-voltage (C–V) curves presented an un-exponential behavior with interesting effects such as an increase of built-in voltage and negative capacitance. Based on the results obtained, the growth method for MWCNT structures was proposed.