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Strain assisted inter-diffusion in GaN/AlN quantum dots
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10.1063/1.4775587
/content/aip/journal/jap/113/3/10.1063/1.4775587
http://aip.metastore.ingenta.com/content/aip/journal/jap/113/3/10.1063/1.4775587

Figures

Image of FIG. 1.
FIG. 1.

(a) RSM of sample A, as grown, indexed with H, K, and L referring to relaxed AlN. Relaxed AlN and GaN positions are shown as white spots at the crossing of white dashed lines. (b) (respectively, c)) are linear scans along H (horizontal black arrow) (respectively, L (vertical black arrow)) at L = 4.9 (respectively, H = 0.98) for as grown (black), annealed at (red) and (blue) samples. Intensities have been averaged over 3 points. (d) is a scheme of the diffraction pattern in thereciprocal space where AlN buffer, GaN wetting layers and uncorrelated GaN quantum dots contributions are represented.

Image of FIG. 2.
FIG. 2.

(a) RSM of sample B, as grown, indexed with H, K, and L referring to relaxed AlN. Relaxed AlN and GaN positions are shown as white spots at the crossing of white dashed lines. (b) (respectively (c)) linear scan along H (horizontal black arrow) (respectively, L (vertical black arrow)) at L = 4.9 (respectively, H = 0.98) for as grown (black), annealed at (red) and (blue), samples. Intensities have been averaged over 3 points. (d) is a schematic representation of the diffraction pattern in the reciprocal space where AlN buffer, GaN wetting layers and vertically correlated GaN quantum dots are represented.

Image of FIG. 3.
FIG. 3.

Anomalous terms of the atomic scattering factor (blue curve) and (black curve) for the A = Ga atoms at energies close to the Ga K-edge, obtained from a fluorescence spectrum (see text). is calculated from using a difference Kramers-Kronig method.

Image of FIG. 4.
FIG. 4.

(a) RSM of sample A, as grown, indexed with H, K, and L referring to relaxed AlN. (b) Linear L-scan (vertical black arrow) at H = 0.98 for as grown (black), annealed at (red) and samples. The red segments show the region of interest (ROI) of the linear detector used for L-scans and DAFS spectra measurement (Fig. 5 ). The DAFS curves in Fig. 5 correspond to the diffracted intensity integrated along the two red segments centred at H = K = 0.98, L = 1.92, and H = K = 0.98, L = 1.96.

Image of FIG. 5.
FIG. 5.

Energy scan across the Ga K-edge (10 367 eV) at fixed (H = 0.98, K = 0.98, L = 1.92) ( ) and (H = 0.98, K = 0.98, L = 1.96) ( ) positions in the reciprocal space. Both experimental (open symbols) and best fit curves (solid lines) are shown for sample A as grown (open circle) and annealed at (open square). The best fit parameters are reported in Table I .

Image of FIG. 6.
FIG. 6.

Extended-DAFS oscillations extracted out of DAFS spectra of sample A as grown (open circle) and annealed at (open square), measured at fixed (H, K, L) reciprocal space units, i.e., (0.98, 0.98, 1.92) and (0.98, 0.98, 1.96), to which correspond 4% and 2% iso-strained regions, together with the best-fit curves (solid lines).

Image of FIG. 7.
FIG. 7.

HR-STEM HAADF images of GaN/AlN QDs heterostructure (sample B), as grown (a) and after annealing at (b).

Image of FIG. 8.
FIG. 8.

HR-STEM HAADF images of GaN/AlN QDs heterostructure (sample A) after annealing at . The zoom in inset shows that interdiffusion extends roughly over half of the spacing between the dots.

Image of FIG. 9.
FIG. 9.

(a) HR-STEM HAADF image after annealing at . Well defined GaN crystallites (bright) are visible in AlN matrix (dark). (b) Corresponding strain map from geometrical phase analysis showing that the crystallites are in perfect epitaxy with the AlN matrix and therefore fully strained. (c) High resolution image taken along the zone axis showing Ga-rich islands embedded in Al-rich matrix.

Image of FIG. 10.
FIG. 10.

Photoluminescence spectra at 4 K of as-grown sample A (black curve) and for three different annealing temperatures: (red curve), (green curve), and (blue curve).

Tables

Generic image for table
Table I.

Crystallographic phase difference and scale factor SD obtained by fitting the cusps of DAFS spectra to Eq. (2) . The Gallium content xGa was obtained by assuming a perfect wurtzite structure.

Generic image for table
Table II.

Sample A. best fit results for interatomic distances of nearest neighbours (NN) (Ga-N) and next nearest neighbours (NNN)(Ga-Ga and Ga-Al) and atomic Ga fraction. Debye Waller factors ( ), which are not reported, are equal to Å for NN pairs and Å for NNN pairs, with relative errors of about 20%.

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/content/aip/journal/jap/113/3/10.1063/1.4775587
2013-01-18
2014-04-23
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Strain assisted inter-diffusion in GaN/AlN quantum dots
http://aip.metastore.ingenta.com/content/aip/journal/jap/113/3/10.1063/1.4775587
10.1063/1.4775587
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