Growth of GaN nanowall network on Si (111) substrate by molecular beam epitaxy
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NANO EXPRESS
Open Access
Growth of GaN nanowall network on Si (111) substrate by molecular beam epitaxy Aihua Zhong and Kazuhiro Hane*
Abstract GaN nanowall network was epitaxially grown on Si (111) substrate by molecular beam epitaxy. GaN nanowalls overlap and interlace with one another, together with large numbers of holes, forming a continuous porous GaN nanowall network. The width of the GaN nanowall can be controlled, ranging from 30 to 200 nm by adjusting the N/Ga ratio. Characterization results of a transmission electron microscope and X-ray diffraction show that the GaN nanowall is well oriented along the C axis. Strong band edge emission centered at 363 nm is observed in the spectrum of room temperature photoluminescence, indicating that the GaN nanowall network is of high quality. The sheet resistance of the Si-doped GaN nanowall network along the lateral direction was 58 Ω/ . The conductive porous nanowall network can be useful for integrated gas sensors due to the large surface area-to-volume ratio and electrical conductivity along the lateral direction by combining with Si micromachining. Keywords: GaN nanowall network, GaN growth on Si substrate, Porous GaN, Hall measurement, N/Ga ratio, TEM
Background GaN semiconductors exhibit excellent properties in optical devices and high-power/high-frequency electronics, such as light-emitting diodes [1], laser diodes [2], and AlGaN/GaN high-electron mobility transistors [3]. Much attention also has been paid to GaN nanostructures because nanoscale materials, such as nanowires [4], nanotubes [5], and nanorods [6], are dislocation-free and strain-free with a large surface area-to-volume ratio [7,8]. Due to these characteristics, GaN nanostructures exhibit superior performance to conventional planar GaN. An optoelectronic device using GaN nanowires was demonstrated in [9]. Though these GaN nanostructures (nanotube, nanowire, and nanocolumn) are exhibiting promising properties, fabrication of an electronic device based on them is complicated because the separation of nanostructures inhibits electric current from flowing among these nanostructures. In the case of a photo detector based on GaN nanowires, the detector was fabricated on an individual nanowire [10]. Fabrication of an electronic device on an individual nanowire is highly difficult. Nanowalls are attractive due to their porous surface and material continuity along the lateral direction. Carbon
[11,12], ZnO [13,14], and NiO [15] nanowalls have been investigated. Kesaria et al. reported the growth of a GaN nanowall network on a sapphire substrate [16-18]. In these papers, transformation among the GaN nanowall network, GaN nanocolumn, and GaN film is observed by changing the growth condition. On one hand, the width of the GaN nanowall is in nanoscale and, in terms of property, is as good as a separated nanostructure [16]. On the other hand, unlike nanotubes and nanowires, the GaN nanowall network is continuous along the lateral direction. Because of this characteristic, the GaN nanowall network is expec
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