Quantum dots are nanostructures of semiconducting materials that behave a lot like single atoms and are very easy to produce. Given their special properties, researchers see huge potential for quantum dots in technological applications. Before this can happen, however, we need a better understanding of how the electrons “trapped” inside them behave. Dresden physicists have recently observed how electrons in individual quantum dots absorb energy and emit it again as light.
Their results were recently published in the journal Nano Letters.
Quantum dots look like miniscule pyramids. Inside each of these nano-pyramids are always only one or two electrons that essentially “feel” the constricting walls around them and are therefore tightly constrained in their mobility. Scientists from Helmholtz-Zentrum Dresden-Rossendorf (HZDR), TU Dresden. TU Dresden and the Leibniz Institute for solid State and Materials Research Dresden (IFW) have now studied the special energy states of the electrons trapped inside individual quantum dots.
Sharp energy levels
The behaviour of electrons in a material essentially determines its properties. Being spatially constrained in all three spatial dimensions, electrons inside a nano-pyramid can only occupy very specific energy levels — which is why quantum dots are also called “artificial atoms.” Where these energy levels lie depends on the chemical composition of the semiconductor material as well as the size of the nano-pyramid. “These sharply defined energy levels are exploited, for example, in highly energy-efficient lasers based on quantum dots. The light is produced when an electron drops from a higher energy level into a lower one. The energy difference between the two levels determines the colour of the light,” Dr. Stephan Winnerl of HZDR explains.