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Microstructural evolution of nonpolar (11-20) GaN grown on (1-102) sapphire using a 3D-2D method
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Image of FIG. 1.
FIG. 1.

AFM images of islands after (a) 120 s and (b) 600 s of 3D growth. The islands are elongated along [0001] and have an anisotropic shape. The image height of (a) is 300 nm and (b) is 900 nm.

Image of FIG. 2.
FIG. 2.

Dark field TEM images of the 600 s islands (a) viewed close to [0001], . The gray arrows indicate dislocations intersecting the island facets at 90°. (b) Dark field TEM images of the 600 s islands viewed close to [1-100], showing that the dislocations are confined to the -plane.

Image of FIG. 3.
FIG. 3.

(a) Dark field plan-view TEM image viewed close to [11-20] of adjacent islands using . A misorientation of 9° is present between the (0001) planes. (b) Selected area diffraction pattern showing a misorientation of 11° between adjacent islands.

Image of FIG. 4.
FIG. 4.

(a) Nomarski phase contrast micrographs of the film coalesced at a V/III ratio of 50 which is free from facetted pits. (b) AFM image of the same film.

Image of FIG. 5.
FIG. 5.

Weak beam dark field TEM images of the film with 600 s 3D growth (a) viewed close to [0001], , and (b) close to [1-100], . The dashed line marks the position at which the dislocation lines start to change direction.

Image of FIG. 6.
FIG. 6.

Variation in dislocation density (filled squares) and BSF density (open squares) with 3D growth time in the coalesced films.

Image of FIG. 7.
FIG. 7.

Variation in BSF length (filled squares) and width of islands (open squares) with 3D growth time (both measured along [1-100]).

Image of FIG. 8.
FIG. 8.

Schematic of the dislocation bending due to the change in growth conditions, viewed along [0001]. (a) Islands are bound by {10-11} facets so dislocations are inclined at 60° to the substrate interface to minimize their line energy. (b) When growth conditions change, the dislocations bend to intersect the (11-20) plane at 90°. (c) When islands are large enough to impinge and coalesce, there is a merging of BSFs in adjacent islands, resulting in a drastic increase in BSF length and annihilation of two of the four partial dislocations.


Generic image for table
Table I.

Mean island heights (measured from AFM images) of islands with different 3D growth times and the correlation with the distance from the substrate interface at which dislocation line direction first changes (in cross-sectional TEM images).


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Microstructural evolution of nonpolar (11-20) GaN grown on (1-102) sapphire using a 3D-2D method