Type of presentation: Poster

MS-9-P-5738 STEM observations of indium segregation in InAlN epitaxial layers

Borysiuk J.1, Sobczak K.1, Kaminska A.1, Jezierska E.2, Yamamoto A.3, Schenk D.4, Suski T.5, Zytkiewicz Z. R.1
1Institute of Physics, Polish Academy of Sciences, Warsaw, Poland, 2Faculty of Materials Science and Engineering, Warsaw University of Technology, Warsaw, Poland, 3Department of Electrical and Electronics Engineering, University of Fukui, Fukui, Japan, 4SOITEC Specialty Electronics, Villejust, France, 5Institute of High Pressure Physics, Polish Academy of Sciences, Warsaw, Poland
borysiuk@ifpan.edu.pl

Indium segregation in high In content InAlN layers grown on GaN/sapphire templates was investigated by scanning transmission electron microscopy (STEM). The chemical nonuniformity of the layers was determined from energy dispersive X-ray analysis (EDX) and high-angle annular dark-field (HAADF) imaging. Low In content samples show no indication of a preferential incorporation of indium, proving that compositionally uniform layers and structures could be grown. For high content of indium, above 20 at % on average, the growth becomes unstable, leading to the preferential incorporation of In at some orientations [1,2]. The V-shaped In-rich structures were observed, resulting in the preferential indium segregation at the sides of the structures (Fig. 1). Indium atoms segregation was usually visible as a bending of lattice planes in InAlN structure. A detailed, structural model of strained defects, based on high-resolution TEM (HRTEM) observations was proposed. The model assumes coherent substitution of aluminum by indium in Al lattice sites which leads to the a-plane compressive stress accumulation. Such stress leads to the vertical strain by upward motion of the neighboring lattice sites and elongation of the c-lattice constant locally. Theoretical (simulated) HRTEM images, taking into account the In concentration variations were generated using JEMS software [3]. The changes of the contrast intensity between different atomic columns with variable In content were compared with the experimental data.

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[3] P.A. Stadelmann, Ultramicroscopy 21 (1987) 131

This work was financed by the resources of National Science Center (Poland) allocated by decisions: DEC-2011/03/B/ST5/02698 and DEC-2012/05/B/ST3/03113.

Fig. 1: HAADF and TEM cross-section images of InAlN layers with indium content of 25% (a,c) and 28% (b,d), respectively.