| Summary: | 碩士 === 東海大學 === 物理學系 === 93 === In this thesis, combining low-pressure metal-organic chemical vapor deposition technology with metal-catalyzed the growth of nanowire onto silicon substrate is the main purpose. We hope to synthesize GaN nanostructure possesses quantum confinement effect.
In this study, 5nm-thick Au thin film used as catalyst for synthesizing nanowires sputtered onto monocrystalline silicon (100). TMG, NH3 and C2H2 gases were used as Ga, N and C precursors respectively. The structural characteristic of the material was examined with scanning/ transmission electron microscope, Raman spectra and X-ray powder diffraction. On the side, the optic characteristic and quantum confinement effect were measured by Photoluminescence spectra.
First, carbon nanotubes (CNT) were used to confine the radial growth simultaneously growth of GaN and carbon nanotube. The presence of the wurtzite structure GaN nanowires encapsulated inside the cavity along the length of a multi-wall carbon nanotube by experiment result. In the experiment, the inner and outer diameters and GaN nanowire encapsulated inside the carbon nanotube were changed with the flow rate of C2H2 was controlled. The outer diameter of CNT is about 20-50 nm and the diameter of GaN nanowire is about 10-15nm while the flow rate of C2H2 was controlled to be 50sccm. The outer diameter of CNT is about 15-20 nm and the diameter of GaN nanowire is about 6-8nm while the flow rate of C2H2 was controlled to be 25sccm. The diameter of GaN nanowire is decreasing with the flow rate of C2H2 reduced and conforms with the inner diameter of CNT as well as the band-gap has blue-shift. Gold can not catalyze the growth of CNT is already knew ago, but we find that the carbon nanotube can be catalyzed by Ga in documents. Hence we suppose the growth of CNT was catalyzed by Ga-Au alloy and the sections of GaN nanowire were caused by the different speed of growth.
On the side, we synthesize GaN nanowire by 2-step method. The first part of GaN nanowire was synthesized at 750℃ and the second part was synthesized while the temperature cooling down. The GaN nanowire was defined to be wurtzite structure from experiment result. The first part of the wire was observed from TEM image that has triangular cross section with 36 nm diameters and the second part of the wire was observed from TEM image that has 5nm diameter. We can not observe obviously the quantum confinement effect from the analysis of spectra due to the second part GaN nanowires are too short. Hence we suppose that the synthesis of second part of GaN nanowire was catalyzed by using the minority of Au was not covered by nitrides as catalyst during cooling down.
In this study, the way of synthesizing GaN@CNT is efficiently to control the diameter of GaN nanostructure. That is efficiently and simply to synthesize a large amount of semiconductor materials possess quantum confinement effect.
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