The work done at the University of Michigan focuses on the effects of lateral FIB patterning and layering on multilayer InAs/GaAs(001) QD structures. Patterning by in vacuo FIB is unique from other patterning techniques because it eliminates exposure of the sample to air between patterning and dot growth. The team found that the size of the FIB-patterned holes and the lateral pattern spacing provide a way to control QD position and dimensions, giving a means of tailoring QD areal density and size.

The patterning conditions could be adjusted so that QDs formed at 100% of the FIB-patterned holes, and did not nucleate away from the holes. Additionally, analysis of the change in QD size as a function of pattern spacing provided a means of estimating the maximum average adatom surface diffusion length for the given growth conditions, a characteristic that can be difficult to measure.

These findings are significant because they provide an understanding of how to use the patterning conditions to achieve a desired QD size and areal density without altering other growth conditions. This is important because the QD dimensions and areal density affect the electronic and optical properties of the QDs as well as their ability to be used for specific applications where these properties are critical. For example, quantum-computing applications may require specific placement of QDs at a low density, while laser or solar-cell applications may desire a very high areal density of QDs with uniform size distribution.

Further details can be found in the journal Nanotechnology.