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Spontaneous and ordered growth of III-N nanorods on polar and non-polar substrates
|Enrique Calleja 1, Javier Grandal 1, Sergio Fernandez 1, Miguel A. Sanchez 1, Jose M. Calleja 2, Eva Gallardo 2, Esperanza Luna 3, Achim Trampert 3, Uwe Jahn 3|
1. ISOM-Dpto Ing Electronica, ETSI Telecomunicacion, Universidad Politecnica de Madrid (ISOM-UPM), Ciudad Universitaria s/n, Madrid 28040, Spain
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.
Presentation: Invited oral at E-MRS Fall Meeting 2009, Symposium C, by Enrique Calleja
See On-line Journal of E-MRS Fall Meeting 2009
Submitted: 2009-07-15 16:56 Revised: 2009-07-16 12:50