Figures

Figure 1

Schematic of the layer structure.

Figure 2

AFM image of sample with 8 % Indium. Surface area: 2 x 2 µm. A smooth surface is found which is typical of the samples, indicating step-flow growth mode. The black dots represent pinholes with a diameter of about 50 nm and a density in the range of 109 cm-2.

Figure 3

Pinhole density as a function of the In content in the InGaN layer.

Figure 4

TEM cross-sectional image of sample with 6 % Indium, (0002) bright-field image. The pinholes lie within the InGaN layer. The InGaN/GaN interface is indicated by horizontal bars. There are no misfit dislocations at the interface.

Figure 5

TEM cross-sectional image of sample with 8 % Indium, (20) bright-field image. Contrast at the apex of the pinholes reveals high stress there (see arrows).

Figure 6

TEM cross-sectional image of sample with 14 % Indium, (20) weak-beam image. Misfit dislocations at a pinhole that reaches the heteroepitaxial interface (on the left). The specimen is tilted around the horizontal axis so that the misfit dislocations lines are visible.

Figure 7

TEM cross-sectional image of sample with 14 % Indium, multi-beam image taken along the [2 0] zone axis. A small pinhole that is not attached to a threading dislocation is visible.

Figure 8

TEM cross-sectional images of sample with 8 % Indium. Left: multi-beam image taken along the [2 0] zone axis; all threading dislocations are visible. Right: (0004) weak-beam image; only threading dislocations with a c-component Burgers vector are visible.

Figure 9

Model of elastic relaxation at pinholes. Left: Fictitious situation with rigid lattice planes. Right: Elastic relaxation.

Figure 10

Nucleation of misfit dislocations by glide of threading dislocations according to the Matthews-Blakeslee model. "A" corresponds to InGaN layer, "B" corresponds to GaN layer. Schematic after [8].

Figure 11

Schematic of slip systems in the wurtzite structure. The basal plane is parallel to the heteroepitaxial interface. The crossed out ticks indicate slip systems that cannot lead to misfit dislocations by glide of threading dislocations. See 4.2 for details.

Figure 12

Peierls force as a function of the ratio of slip plane distance d and length b of the Burgers vector for the slip systems illustrated in Figure 11.

Figure 13

Calculated critical thickness hc of the InGaN layer as a function of the In content for nucleation of misfit dislocations by glide of 1/3<110>||{101} threading dislocations according to the Matthews-Blakeslee model. On the right, three curves are shown, representing threading segments with different edge components (pure screw; segment running straight in the slip plane; large edge component). For the calculation of the fourth curve, the Peierls force has been neglected.

Figure 14

Schematic of plastic relaxation at deep pinholes that reach the heteroepitaxial interface, as observed in the sample with the highest In content of 14 %. Left: Cross-sectional schematic view of a deep pinhole, parallel to the heteroepitaxial interface (lower horizontal line). Right: Perspective view showing how the misfit dislocations glide away from the deep pinholes.

© 1998 The Materials Research Society