Low and high indium fluctuation in MOCVD grown InGaN/GaN as determined by quantitative HRTEM
|Pierre Ruterana 3, Protima Singh 3, Florence Gloux 3, Slawomir Kret 1, E K. Suh 4, Pawel Dluzewski 2, Euijoon Yoon 5|
1. Polish Academy of Sciences, Institute of Physics, al. Lotników 32/46, Warszawa 02-668, Poland
The knowledge of local strain fields associated with defects is important for the determination of the local atomic configuration. This is particularly the case in GaN based heterostructures where densities of defects are large, and the correlation between properties and structure needs to be understood. Image processing and image simulations help to extract quantitative information. In this work, we discuss our results on InGaN/GaN quantum wells. For the GaN/InxGa1-xN/GaN QW’s, the mechanism of the light emission is not yet clearly understood. Narukawa et al. suggested that indium rich cluster may help to localise the carriers and will be a centre for radiative recombination. Using pattern recognition on HRTEM images, Kisielowski et al. have shown that the indium may segregate into 1-3 nm diameter areas inside the QW. Ruterana et al., based on a strain distribution extracted from HRTEM images and 2D FEM modelling, pointed out that the In composition fluctuation areas may depend on the growth technique. In this work, two types of samples were investigated, in the first, the measured strain was always high, the thickness of the wells being in the 3-5 nm range. The second set of samples was prepared as pure InN/GaN quantum wells, with thicknesses in the range of a few monolayers, we find that the exctrated local strain does not reflect the nominal composition in these structures and we suggest the origin of the discrepency. In the two types of structures, the In composition fluctuations are clearly pointed out from the HRTEM observations. By a combination of 3D FEM and HRTEM observation, we show that the observed samples exhibit indium composition fluctuation. In many instances, the indium content can reach x=1 in the clusters inside the core. In these MOCVD QWs, we attempt to connect the Quantum dot density, composition, and shape, to the growth conditions.
Presentation: invited oral at E-MRS Fall Meeting 2005, Symposium A, by Pierre Ruterana
See On-line Journal of E-MRS Fall Meeting 2005
Submitted: 2005-05-30 07:57 Revised: 2009-06-07 00:44