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Causes and elimination of pyramidal defects in GaSb-based epitaxial layers
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Image of FIG. 1.
FIG. 1.

(Color online) Ehrlich–Schwoebel barrier has a destabilizing effect on islands. Here, the adatom step barrier promotes the growth of pyramidal structures on the surface.

Image of FIG. 2.
FIG. 2.

(Color online) Ehrlich–Schwoebel barrier can act as a stabilizing force during epitaxial growth on stepped surfaces. The steps that are wider (narrower) than normal receive more (less) adatoms. This promotes uniform step sizes in the long term.

Image of FIG. 3.
FIG. 3.

(Color online) AFM image of GaSb wafer after oxide removal. The vertical axis is inverted so the pits appear as peaks. This pitting is due to the SbO reacting with the GaSb surface.

Image of FIG. 4.
FIG. 4.

(Color online) AFM images of GaSb surfaces with no AlAsSb layers at three thicknesses: (a) 30 nm, (b) 200 nm, and (c) 650 nm. Defects grow in size, both laterally and vertically, but decrease in density as layer thickness increases.

Image of FIG. 5.
FIG. 5.

(Color online) AFM image of (a) 1 m and (b) 2 m GaSb layers. By the time, 2 m of material has been grown and the density of defects has dropped considerably.

Image of FIG. 6.
FIG. 6.

(Color online) AFM image of 200 nm GaSb with no AlAsSb layer. Notice the clearly defined pyramidal structure of the defects as well as the isolation of the layer structure of the defects from the step flow pattern of the underlying epilayer.

Image of FIG. 7.
FIG. 7.

(Color online) AFM image of buffer layer consisting of 150 nm GaSb, 30 nm AlAsSb, and 500 nm of GaSb. Vertical scale is truncated to emphasize good step-flow pattern; full scale is 0–0.79 nm.

Image of FIG. 8.
FIG. 8.

(Color online) AFM images of regrown GaSb surfaces. Both images are 200 nm of GaSb grown on a previously grown wafer consisting of 150 nm GaSb, 30 nm AlAsSb, and 500 nm GaSb. In (a), the wafer was allowed to develop an oxide layer in between the first and second growths; in (b), the sample was kept under vacuum to prevent an oxide layer from forming. Vertical scales are truncated to show fine detail. Full scale for each is 5.2 and 1.24 nm, respectively.

Image of FIG. 9.
FIG. 9.

(Color online) AFM image of surface of 2000 nm of GaSb grown on 150 nm of GaSb and 30 nm of AlAsSb. The surface is nearly defect-free and shows visible step flow growth. The vertical scale has been truncated. Full scale is 1.6 nm.

Image of FIG. 10.
FIG. 10.

(Color online) AFM images of 30 nm of AlAsSb on top of 150 nm of GaSb. There is no sign of step-flow visible in the AlAsSb; the defect density is also elevated compared to growth of just GaSb.

Image of FIG. 11.
FIG. 11.

(Color online) RHEED oscillations during growth of GaSb and AlAsSb layers. Curves have been offset for clarity. The reduced damping of the minima in the AlAsSb RHEED curve indicates a reduced amount of step progression during growth of that material.

Image of FIG. 12.
FIG. 12.

(Color online) AFM image of 20 nm of GaSb grown on top of 150 nm of GaSb and 30 nm of AlAsSb. Step-flow growth has returned, though the defect density is still elevated compared to pure GaSb growth. However, the pyramids are significantly less isolated. This reduction in isolation speeds the smoothing of the surface, as can be seen in the 5 by 5 m image (b). The step-flow pattern bends around the defects but is not isolated from them as it was prior to the insertion of the AlAsSb. Vertical scales are truncated to show detail; full scale is 3.9 nm for (a) and 2.7 nm for (b).

Image of FIG. 13.
FIG. 13.

(Color online) Reduction in isolation of defects as the GaSb thickness increases. At 650 nm of GaSb with no AlAsSb layer, there is evidence of some reduction in isolation between pyramids and surface (a). By the time 1 m has been grown, there is a significant reduction in the pyramidal nature of the defects (b).


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Causes and elimination of pyramidal defects in GaSb-based epitaxial layers