W.If physicists describe complex phenomena in solids and other multi-particle systems, they often resort to unconventional approaches. In doing so, they sometimes pretend that the material contains atomic nuclei and electrons in addition to other imaginary particles, which they call quasiparticles. According to their true counterparts, they are assigned physical properties such as mass, energy, or momentum. With semiconductors, complex processes can be seen suddenly – such as those that occur in semiconductors. Phantom particles are not only used for theoretical considerations, but also to develop new types of electrical and optical components for the electronics of tomorrow. Scientists from the Lausanne Polytechnic got one three years ago A semiconductor transistor was introduced where a special type of quasiparticle flows for the first time in place of electrons, the so-called excitons.
Excitons consist of a negatively charged electron and a positively charged electron in a crystal lattice, also called a hole. These pairs of electronic holes are constructed into one SemiconductorsWhen an electron from an atom absorbs a photon (such as a laser beam) and enters a higher excited energy state. Exitons do not usually last long. Usually electrons and holes separate from each other instantly, or “fuse” into each other, at which point a light amount is released. Because of their brittleness, it was only possible for a long time at extremely low temperatures to maintain a large influx of excitons in semiconductors. Under these conditions, the electron and hole move only slowly and have a chance to form a bonding state for a long time.
The fact that the exciton transistor developed by Andras Kiss researchers also operates at room temperature relies on using two extremely thin layers of tungsten diselenide (WSe2) and molybdenum disulfide (MoS2) stacked on top of each other. Electrons and holes are formed – by the radiation of light – in a different layer of semiconductors. “The excitons in these materials have a particularly strong bond, and most importantly, they do not dissolve quickly at room temperature,” says Cassette.
Since excitons are not electrically charged, they do not migrate towards a positive or positive electrode like electrons or holes. In order to be able to manipulate quasiparticles, researchers use their electrical dipole moment. This quantity, also known as polarization, arises from the spatial separation between positive and negative charge. It causes the excitons to always move to where the electric field strength is greatest. Because the energy of excitons is the lowest.
The sack of behavior compares it to balls that always seek depressions in hilly and hollow landscapes. “In our first transistor, the excitons tended to fall into the ‘holes’ and not come out,” says Case. To prevent this and to increase the life of the quasiparticles, the researchers inserted a middle layer of hex boron nitride (h-BN) between two layers of tungsten and diselenide molybdenum. This structure effectively reduces the depth of the holes. In this way, the Swiss researchers were able to increase the conductivity of excitones in their system.
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