Optical, Structural, and Electronic Properties of III–V Quantum Dots on Silicon – QDonSi

Consortium partners:

Wrocław University of Science and Technology
Łukasiewicz Research Network – PORT Polish Center for Technology Development

Rapid data transmission and processing underpin today’s information-based society. Most communication now relies on optical channels, where light functions as the information carrier. A global network of optical fibers connects continents, countries, cities, and individual homes.

The continuously growing demand for increased processing and data transfer speeds calls for the next technological breakthrough—replacing electrical connections between computers and their subsystems (such as memory buses) with optical connections, or even fully replacing electronic devices with photonic ones, where photons take over the role of electrons as information carriers.

Although integrated photonic circuits—key components of photonic devices—are already available, a true technological leap requires a cost-effective solution that supports mass production. This condition can only be met by technologies compatible with CMOS (Complementary Metal-Oxide Semiconductor) silicon-based manufacturing platforms currently used for electronic integrated circuits, such as processors.

However, silicon’s inherent material properties pose significant challenges. Its indirect bandgap makes light emission extremely inefficient. As a result, additional semiconductor compounds must be incorporated into devices. Quantum dots made of group III–V elements, such as InAs/GaAs or InAs/InP, are considered the most promising candidates. To keep costs low, the fabrication process must be monolithic—avoiding the assembly of separately manufactured components.

This requirement introduces further complications. III–V materials have much larger lattice constants than silicon, which introduces strain during growth, leading to low crystallographic quality of heterostructures. Moreover, large differences in thermal expansion coefficients cause cracking during cooling of structures grown at elevated temperatures. Both factors generate numerous defects in III–V quantum dots grown on silicon, significantly reducing their emission efficiency.

The research objective of the project is to investigate the material properties of III–V quantum dots on silicon substrates using atomic force microscopy, transmission electron microscopy, and X-ray diffraction to determine structural parameters such as crystallographic quality, defect concentration and types, strain distribution, morphology, and chemical composition.

Subsequently, complementary optical spectroscopic techniques will be used to determine their emission properties, focusing in particular on the role of defects. These tools will allow analysis of the dynamics of physical processes occurring in these cutting-edge nanostructures. Experiments will be performed both on ensembles of quantum dots—where the response is averaged over the entire population—and at the single-dot level, where single-photon emission is recorded. This approach is essential for potential quantum communication applications.

The obtained results will be compared with theoretical models of the band structure of the studied materials. Quantum dots fabricated using two approaches will be investigated: (i) those grown with intermediate buffer layers and a defect-filtering layer to mitigate strain effects and suppress defect formation in the active region, and (ii) those placed directly within the silicon matrix using a core–shell architecture, where defects accumulate at the shell–silicon interface, leaving the emitting core defect-free.

The information gathered throughout the project will help determine whether InAs/GaAs(InP) quantum dots grown on or embedded in silicon can achieve crystallographic quality and optical properties comparable to III–V quantum dots grown on native substrates—an essential milestone for their future use in integrated photonic circuits.

Comprehensive optical and structural characterization carried out during the project will provide extensive insights into the largely unexplored material properties of the investigated quantum dots.