Thesis presented June 29, 2010
Abstract: The work presented in this thesis deals with the growth mechanisms of nitride semiconductor nanowires produced by plasma-assisted molecular beam epitaxy (PA-MBE). The following experimental techniques were used to support the investigations: scanning electron microscopy (SEM), transmission electron microscopy (TEM), multi-wavelength diffraction experiments and spectroscopy in diffraction condition (performed on beamlines BM2 & BM32 at the ESRF), and photoluminescence experiments.
The nucleation of gallium nitride (GaN) nanowires initiated on a 3nm thin epitaxial layer of aluminum nitride (AlN), which is grown on a (111) silicon substrate has been investigated. It is demonstrated that the full relaxation of the nanowires precursors is one of the key points of the GaN nanowires nucleation process. It is furthermore demonstrated that the granular morphology of the AlN buffer plays a crucial role.
Further growth of GaN nanowires in the steady state regime following the nucleation stage has been studied. It has been established that Ga diffusion on the growth plane and on the nanowire side facets is responsible for the growth of GaN nanowires. It has been shown in particular that In may play the role of a surfactant and promote in-plane Ga diffusion, making possible the growth of GaN nanowires at relatively low temperature. Based on the understanding of GaN nanowires nucleation and growth, the PA-MBE growth of AlN nanowires deposited on a 4nm thick SiO
2 layer on Si (001) has been studied, for the first time.
Next, strain relaxation in AlN/GaN super-lattices grown on GaN nanowires has been studied. Comparison with theoretical simulations allows us to conclude that strain relaxation occurs elastically.
Finally, the subject of AlGaN nanowire growth is briefly introduced.
Keywords: Nanowire, Nitride, MBE
On-line thesis.