Researchers find ultra-light-sensitive material for use in optical computers

ITMO researchers have discovered an ultra-light sensitive material. Furthermore, they were able to identify a parameter that will help find other structures with high refractive coefficients. This discovery will take us one step closer to developing compact and efficient elements for optical computers: lasers, chips and sensors. The research is published in Nanophotonics.

The demand for more powerful and advanced computers is growing every year. The problem with conventional ones, however, lies in the electrons that play an important role in them. In any structure crossed by an electric current, there is a risk of overheating, which creates fundamental limitations on the minimum size of the calculation elements. A solution to this problem lies in optical computers that will process the information transmitted by the movement of photons that do not heat up, unlike electrons.

“We will soon reach the limit when any further modernization of electronic machines does not allow for the necessary increase in efficiency. To start using optical computers, we need to create chips and lasers of comparable size. We need materials with high refractive coefficients to develop optical elements on nanoscale. The refractive coefficient tells us how well a structure reacts to light. If its interaction with light is poor, the device will work accordingly, “explains Anton Shubnic, a student at ITMO’s Faculty of Physics and Engineering.

There aren’t many highly light sensitive materials. One of these is silicon (Si), with a refractive coefficient of 4. There are no known materials with a higher refractive coefficient in the visible range. Furthermore, the researchers admit, it is not entirely clear where they can be looked for. After extensive mathematical calculations, ITMO University physicists were able to identify a parameter that could indicate the speed at which light would pass through a semiconductor before physical experiments or complex computational models. This parameter depends on the electronic properties of a material: its band gap and the effective mass of an electron.

“We have focused our attention on semiconductors. These materials have band gaps, which are known for most of them and are used frequently. In optics, the band gap determines the maximum wavelength at which a material remains transparent. The second parameter is the effective mass of the electron. When interacting with other particles in a material, the electrons would act as particles with a different mass than they originally have “, explains Ivan Iorsh, head of the International Laboratory of Photoprocesses in Mesoscopic Systems at ITMO University .

The band gap is an energy range that electrons cannot have in a certain material. If the energy of a photon is less than the band gap, the light can diffuse into the material and if the energy is greater, the light will be absorbed. In optics, the band gap determines the maximum wavelength at which a material remains transparent. This parameter is known for many materials and is actively used. The second parameter is the effective mass of the electron. When interacting with other particles in a material, electrons act as if they have a different mass than they originally have. And this new mass is known as the effective mass.

The theoretical model has shown that the higher the ratio of these two parameters, the higher the refractive coefficient should be. First, the researchers tested their hypothesis on known materials such as silicon and then turned to the less studied ones. As a result, they discovered rhenium diselenide (ReSe₂), a very promising material for optical elements. It turned out that ReSe₂ it has a refractive coefficient from 6.5 to 7 in the visible range, which is significantly higher than that of silicon.

Now, the researchers are planning to launch a global search through open databases of the electronic properties of materials to find other substances with a high refractive coefficient previously ignored by optics specialists.