Thesis presented October 27, 2008

Abstract:
This work reports the metal-organic vapor phase epitaxy of III-Nitride wire- or pyramid-shaped nanostructures and focuses on the growth mechanisms related to these two types of GaN nanostructures. A complete parametric study is presented in order to optimize and to understand the catalyst-free self-assembled GaN nanowire growths. We demonstrate that the silane flux injection is a key-parameter for nanowire growth thanks to the formation of SiN_x passivation layer along the sidewall facets that acts as a mask favoring the vertical growth. A novel silane-free nanowire growth is also proposed in this work using ultra-low precursor flux that favors the formation of vertical facets. Such nanowires exhibit excellent structural and optical properties due to the absence of silicon. In addition, the polarity is found to play a key-role for GaN nanostructure growth, since the nanostructure shape can be basically determined by the polarity orientation: N-polar nanostructure results in wire, whereas Ga-polar in pyramid. Consequently, the shape wire/pyramid of nanostructure can be chosen depending on the polarity control on sapphire or GaN substrates. This method is applied to get ordered arrays of GaN wires and pyramids using selective area growth on patterned mask. Such nanostructures can be used as template for InGaN/GaN heterostructure growth to get either non-polar multi-quantum wells along the wire sidewalls or InGaN quantum dots at the pyramid apex.

Keywords:
Photonics, Heterostructures, Nanowires, Nitrides, Crystal growth

On-line thesis.