Chapter 2 - Migration-enhanced Epitaxy for Low-dimensional Structures

Abstract

Migration-enhanced epitaxy has been applied to grow semiconductor nanostructures by area-selective epitaxy. Even using the solid-source molecular beam epitaxy, successful area-selective growth has been achieved on SiO2 masked GaAs substrates, small discs, pyramids, and nanowires of III-V compound semiconductors have been fabricated. Facet formation process has been investigated using SiO2 mask with stripes in various directions. The area-selective growth on radial stripe patterns revealed that no essential growth takes place in the {110} directions. These results are directly related to the facet formation process around the minute structures. General rule for facets formation suggests that the facet angle is quite sensitive to the V/III flax ratio as well as the substrate orientation. Using area-selective epitaxy, exact positioning of tiny structures can be achieved. However, it is not possible for quantum dots with nanometer sizes, because the mask size cannot be made so small. This problem has been solved by combining the area-selective growth of GaAs pyramids and self-assembled growth of InAs nanodots on the top of the pyramids. Quite narrow photoluminescence line has been observed from the single quantum dots.