The growth of self-assembled and ordered III-N nanorods by Plasma-Assisted MBE is addressed. The nucleation stage and the subsequent nanorod growth are explained considering the growth conditions and the lattice mismatch between the substrate and the nanorods. A strong lateral to vertical growth rate anisotropy is caused by a very fast ad-atom diffusion along the nanorods sidewalls. A significant change of this anisotropy occurs when Al atoms are incorporated to the growth (AlGaN nanorods), as it is clearly distinguished in TEM pictures. This effect, related to a slower Al ad-atom diffusion along the nanorod sidewalls, allow the formation of Quantum Dots (QDs) embedded within the nanorod (GaN/AlGaN).

Nucleation may proceed via Volmer-Weber or Stranski-Krastanov mechanisms depending on the initial lattice mismatch between the nanorod material and substrate. A high initial mismatch (i.e. GaN on bare Si) leads to isolated, well defined nanorods, whereas a smaller one (i.e. GaN on AlN buffered Si) produces a mixture of nanorods and a “faceted matrix” of continuous, rough material. A description of the process to be followed in order to avoid this “faceted matrix” is also presented.

Wurtzite InN nanorods have been grown along the c-plane, on Si(111) substrates, and along the a-plane on m-plane GaN/r-plane sapphire templates. In the second case, a well defined a-plane orientation is determined by HR-TEM and from the dependence of the E2 Raman mode with the polarization angle. HR-SEM pictures reveal top nanorod surfaces showing a- and m- plane facets. PL measurements at low temperature give an emission energy of 0.69 eV, a typical signature of a high quality material. As in the case of c-plane oriented III-N nanorods, no wetting layer is observed, in marked contrast with the nucleation and growth of QDs.

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1. MBE growth and characterization of InN-based layers and nanostructures for infrared applications
2. Investigation of InN layers grown by molecular beam epitaxy on Si or GaN templates
3. Low frequency noise measurements in InN films
4. Optical properties of InN grown on Si(111) substrate