New Properties of Excitons Discovered That Can Lead to Energy-Efficient Electronics

The dual nature of excitons may replace semiconductors for more efficient electronics.

The scientists from EPFL's Laboratory of Nanoscale Electronics and Structures (LANES) have shown impressive leaps of advancements in the field of Nanoelectronics. The team particularly handles excitons, a state of high energy electrons along with their stable state electron holes.

To explain detail, when an electron gains sufficient energy, the electron will jump up to a higher energy level. When this happens, the electron will leave a hole or a void, which will be positively charged.

This creates a duality of positive charge and negative charge.

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The first major breakthrough by the scientists was their ability to control the exciton flow in room temperatures.

Now, the same team has made another discovery, excitons could change the properties of light that is incident on them.

When a light beam falls on the excitons, minor changes in the orientation of the excitons can change properties likes polarization and intensity.

These properties are very advantageous in the field of electronics as excitons can help in building transistors that run cooler and more efficient than what we use today.

Excitons mainly exist in insulating and semiconducting materials. 2D materials are the most efficient structures which allow the study of excitons.

The EPFL scientists thus focused their research on these 2D materials and studying their properties.

When two 2D materials are combined, they exhibit quantum properties that neither material has. Hence, the scientists combined tungsten diselenide (WSe2) with molybdenum diselenide (MoSe2) to create a combination that would show enough quantum properties so that the scientists could actually gauge it.

The scientists then used a laser beam having circular polarization and targeted it towards the combination of these two-dimensional materials.

When the position of the 2D materials was shifted to create a moiré, it caused the polarization of the light to change, which was initially in circular polarization.

By carefully shifting the 2D materials, scientists were able to alter not just the polarization, but also the wavelength and intensity of the light.

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Excitons New Properties Discovered
Source: LANE EPFL

The explanation to why the properties of light change with a change in orientation of the 2D materials lie in a property within excitons called valley. A valley is developed by the extreme energy states produced by the exciton.

The higher and lower states produced by the valleys can be used to process information just like a semiconductor as both works the same way by alternating between higher and lower energy states.

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"Linking several devices that incorporate this technology would give us a new way to process data. By changing the polarization of light in a given device, we can then select a specific valley in a second device that's connected to it. That's similar to switching from 0 to 1 or 1 to 0, which is the fundamental binary logic used in computing" said Andras Kis, head of LANES.

The technology might be in its early stage, but we may see it progress through the years to come and it might even replace the building blocks of electronics that we use today.

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