A recipe for making perfectly ordered quantum dots

Researchers from the Johannes Kepler University in Linz, Austria, have shown that they can grow uniformly sized quantum dots on pit-patterned substrates with inter-dot distances varying from a few hundred nanometres to several microns on one and the same sample….

Researchers from the Johannes Kepler University in Linz, Austria, have shown that they can grow uniformly sized quantum dots on pit-patterned substrates with inter-dot distances varying from a few hundred nanometres to several microns on one and the same sample. Being able to accurately control inter-dot distances in this way will be useful for making a variety of electronic and optoelectronic devices with novel functionalities, such as single photon emitters.

Quantum dots in pits

The researchers began by defining the most important parameters for molecular beam epitaxy growth of strictly ordered germanium dots on pit-patterned silicon substrates. They then showed that these growth parameters are closely linked and need to be adjusted with respect to each other for optimal growth. Indeed, the initial pit shape and size, as well the growth conditions of the Si buffer layer, have to be adjusted to provide suitable preconditions – or a solid foundation – for the growth of Ge quantum dots with the desired size, composition and nucleation position.

Ordered quantum dots

The team also showed that the two-dimensional Ge wetting layer between pits can act as a stabilizer that prevents the dots from changing shape and inhibits the formation of dislocations in ordered dots. These findings allow perfectly ordered and homogeneous Ge dots to be fabricated on one and the same sample, even if the pit-period is varied from a few hundred nanometres to several microns.

Finally, by showing that the growth of InAs dots on GaAs substrates can also be controlled in this way, the researchers say that many aspects described in their work might be of great use when growing ordered epitaxial quantum dots made from other materials, such as different group III-V semiconductors.

More details of the work can be found in the journal Nanotechnology.

About the author
The studies were carried out at the Institute of Semiconductor and Solid State Physics at the Johannes Kepler Universtiy, Linz (JKU). Martyna Grydlik is currently a post-doc at the Leibniz Institute for Solid State and Materials Research, Dresden (IFW). Gregor Langer is working as a research scientist at Recendt, the Research Center for Nondestructive Testing GmbH. Thomas Fromherz is group leader and Friedrich Schäffler is a full professor at the Institute of Semiconductor and Solid State Physics at the JKU, Linz. Moritz Brehm is currently Erwin Schrödinger fellow of the Austrian science funds FWF, working at the IFW in Dresden. Martyna Grydlik and Moritz Brehm contributed equally to the work by designing and fabricating the samples, carrying out the experiments, the statistical analysis and writing the manuscript. Gregor Langer fabricated part of the substrate templates and contributed to their design.