dc.description.abstract | This dissertation includes the self-designed home-made chemical-beam epitaxy system, the methods of synthesizing gallium nitride nanorods and indium nitride nanorods without catalyst, and the discussion of detailed optical properties of indium nitride nanorods.
The chemical-beam epitaxy can be work in high vacuum circumstances at high temperature with low fabrication cost. Three-axle z-axis manipulator provides stable rotation capability and flexible expansibility. The design of heat module is able to work at high temperature up to 1100oC without harming the surrounding components. Group-V source is supplied by nitrogen plasma, which is beneficial for indium nitride growth. Group-III metalorganic sources are introduced into the growth chamber by a special designed gas source ring, which makes the reactants hinge on the substrate surface efficiently and uniformly.
The growth of dislocation free GaN nanorods on c-sapphire substrates by a CBE technique is demonstrated. By compared the CBE method with other common growth methods, the CBE is a more feasible technique to fabricate high-quality, high-density, and vertical-alignment GaN nanorods. Without extra metal catalyst required, the thickness and length distributions of each GaN nanorods were formed identically. Furthermore, the nanorods were grown epitaxially and were elongated in the direction parallel to the surface normal.
In addition, the InN nanorods were prepared using the same chemical-beam epitaxy without a catalyst. The nanorods are grown nearly unidirectionally with diameters ranging from 20 nm to 40 nm, depending on the In/N flow ratio between 0.4 and 0.7. XRD and TEM results show that these InN nanorods are single phase wurtzite crystals with preferred orientation along the c-axis. Raman spectrum reveals two clear peaks, which correspond to the (high) and (LO) modes, respectively.
The optical properties of InN nanorods was followed investigated by using PL measurement and Raman spectroscopy. The emission peaks of PL spectra range from 0.69 to 0.79 eV, showing a blue shift as the rod size decreases from 40 to 5 nm. The Raman spectra of the nanorods exhibit only two active phonon modes, i.e. (high) and (LO), at 491 cm-1 and 593 cm-1, respectively. These two peaks do not shift with rod size, indicating the residual strain as well as the carrier concentration in the nanorods of different sizes is about the same. That obviates the influences of strain and the Moss-Burstein effects on spectral shifts. On the other hand, theoretical calculation based on a finite depth square well model reveals the possibility of quantum size effect on the observed size-dependent PL shifts. | en_US |