Site specific growth oF ZnO rods using low pressure chemical vapour deposition technique
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Date
2016-06
Authors
Wong Si Min
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Abstract
Zinc oxide (ZnO) is a semiconductor material that has unique properties, such as wide direct band gap of 3.37 eV and high exciton binding energy of 60 meV at room temperature. This makes the ZnO as a potential candidate for field-effect transistor, photodetectors, sensor devices and light emitting devices applications. These nanoscaled devices require a very delicate fabrication process to ensure its excellent performance. However, the current challenge in the fabrication of semiconductor nanodevices based on the bottom-up approach is the ability to grow the ZnO rods at the desired location on the substrate. In this work, the low pressure chemical vapour deposition (LPCVD) techniques has been used to synthesize the site-specific growth of ZnO rods. The effect of substrate distance from Zn powder, amount of Zn powder and synthesis duration on the growth of ZnO rods were studied systematically. The determined optimum parameters are placing the substrate at 5 cm away from Zn powder, 30 min of synthesis duration at 650 °C by using 0.5 g of Zn powder. The ZnO rods have average length, diameter, aspect ratio and area density of 869.53 nm, 360.55 nm, 2.52 and 5 rods/ μm2. The growth mechanism of the ZnO rods was investigated. The synthesized ZnO rods were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM) to gain the understanding on the growth of ZnO rods. It was found that the Au thin film/Si substrate which furthest away from the Zn powder source was more favorable for the growth of Au-catalyzed ZnO nanorods. The growth of Au-catalyzed ZnO nanorods were governed by the vapour-liquid-solid and vapour-solid (VLS-VS) mechanism. While, the ZnO rods grown on the ZnO seed layer/Si substrate was found that when the substrate was exposed to a larger amount of Zn powder (located nearer to Zn powder or used larger amount of Zn powder) and longer synthesis duration would result in very large diameter and long ZnO rods. Only VS mechanism was involved in the growth of self-catalyzed ZnO rods. The patterning of ZnO seed layer/Si substrate was performed. The ZnO rods were then grown by LPCVD on the patterned ZnO seed layer/Si substrate. The increasing of etching time could lead to a better site-specific growth of ZnO rods.