Formation mechanism of volcano-like structural defects in multiple periods of InAs quantum dots on GaAs

Studies on detailed formation mechanisms of volcano-like structural defects on 20 periods of InAs quantum dots on a GaAs substrate grown by molecular-beam-epitaxy system were carried out by microstructural examinations with high-resolution transmission electron microscopy. The volcano-like structure has started to be formed through the wave-like modulation of the growth surface mainly caused by the gradients in the surface chemical potential. Considerable retardation of growth has occurred and a deep valley is formed inside the structure and the width of a fully grown structure has reached 100 nm. The extensive growth competition between quantum dot structure and volcano-like structure has also occurred in the area where the changes of curvature are large. A spinodally decomposed structure has formed inside the defect whose wavelength of modulation is initially in the [1 1 1] direction, reflecting the initial inclined surface profile, and then changed to the [1 1 0] direction as growth time goes on from the bottom of the structure. This means that the modulated structure has revealed the structure far from the equilibrium state.