Transmission-electron microscopy study of the shape of buried ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ quantum dots

High-resolution electron microscopy, on-zone bright-field imaging, and image simulation were used to investigate the shape of capped ${\mathrm{In}}_{0.6}{\mathrm{Ga}}_{0.4}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ semiconductor quantum dots. Cross-section 〈110〉 high-resolution images suggest that the quantum dots are lens shaped, while the [001] on-zone bright-field images show a contrast that suggests a quantum dot morphology with four edges parallel to 〈100〉. The image simulation, however, suggests that a spherical quantum dot can produce a square-shaped image. These observations lead to the conclusion that the quantum dots in buried ${\mathrm{In}}_{0.6}{\mathrm{Ga}}_{0.4}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ semiconductor heterostructures are lens shaped.