An advance by Miyamoto and his colleagues could prove useful in high-performance photonic devices, such as vertical cavity surface emitting lasers. Multi-stacking quantum dots improves optical gain by increasing dot density. Self-organizing is a key technology for forming the dots, but it relies on strain that results from the lattice mismatch of the dot material on the substrate. It is therefore subject to limits imposed by crystal defects and by the increased variation in dot size caused by accumulative strain. Miyamoto and his colleagues have addressed those limitations with gallium nitride arsenide (GaNAs) that has strain opposite that of indium arsenide deposited on a gallium-arsenide substrate.

The researchers inserted the GaNAs semiconductor as a spacer between the dot layers and investigated the resultant multi-stacked dot structures with photoluminescence and transmission electron microscopy. Their findings verified a reduction in luminescence line width, an increase in emission intensity, and an improvement in dot uniformity, even with an extremely small spacer thickness.