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2023. 05. 29 -

Thinner than a hair, as powerful as a laser: a new invention by FTMC physicists

(Square quantum superlattices and a human hair on the right. Photo: Vladislovas Čižas / FTMC)
A team from FTMC Departments of Optoelectronics has patented an invention called "Plačiajuostę aukšto dažnio spinduliuotę generuojantis / stiprinantis įrenginys, naudojantis puslaidininkines supergardeles (eng. Broadband high-frequency radiation generating / amplifying device using semiconductor superlattices"). The possibility of such a device was theorised 30 years ago. But Lithuanian scientists were the first in the world to prove it in practice.
The invention has been approved by the The State Patent Bureau of Lithuania and an application has been filed to the European Patent Office. The latter process could take up to a year due to bureaucratic procedures - but for now, let's see what the benefits of these superlattices are.
Amplifies the signal up to a thousand times
"The authors of this invention are Prof. Gintaras Valušis, Dr. Kirill Alexeev, Dr. Natalia Alexeeva, Dr. Linas Minkevičius, Dr. Dalius Seliuta ... Very great people. And me", laughs Vladislovas Čižas, a PhD student at FTMC and one of the authors of the invention. His PhD topic is also related to the invention.
The physicist says that FTMC has recently been focusing on the development of quantum semiconductor devices, and this is one of the results of this activity: the Lithuanians have shown that it is possible to generate or amplify some electromagnetic waves in a new way - by means of quantum superlattices.
(PhD student Vladislovas Čižas. Photo: FTMC)
"We can choose a very wide range of frequencies, from gigahertz (which is what Wi-Fi, 5G, 6G, etc. are) to terahertz, which is what most of our department is researching. And terahertz is promising at improving of airport security systems, medical research or explosives detection," says Vladislovas.
Quantum superlattices serve as a source or "amplifier" for these electromagnetic waves. In some cases, this invention can produce a signal up to a thousand times stronger than normal! The more powerful the radiation, the better the quality of the research.
"What can we do? By adjusting the applied voltage, we produce different excitations of the required frequencies, which are very powerful, even comparable to lasers. We also have more possibilities to choose which frequencies of electromagnetic waves we want to generate. Lasers normally produce simple waves or harmonics (waves frequency multiplied by two, three, etc.). But with our invention, we can also excite so-called fractional frequencies - 5/3 of a frequency, etc.
This further extends the applications of these waves", says FTMC researcher.
V. Čižas suggests imagining a simple battery: connect a superlattice to it, start to generate a very weak excitation signal, and the superlattice will amplify it up to a hundred or thousand times. Or it will "create" the harmonics and fractional frequencies mentioned above from that signal.
"This is another new type of gigahertz and terahertz wave source," explains Vladislav. - The problem with terahertz sources is that they are either weak or expensive. And ours is comparatively cheap. Obviously, it's not about buying a light bulb, but the invention balances between low cost and quite high potential."
(Square quantum superlattices and a human hair on the right. Photo: Vladislovas Čižas / FTMC)
We'll need a microscope here
Okay, but what do these superlattices look like?
As is often the case at FTMC, we are talking about very small sizes. V. Čižas pulls an example out of a drawer: with the naked eye, you can see a rectangular crystal that is ten times smaller than a square box in a math notebook.
"So, there are fifteen superlattices in that dot," smiles the scientist. The square lattices themselves are thinner than a human hair (Vladislovas took a special microscope picture of it for us) and are made of gallium arsenide crystal. Specifically, Dr. Renata Butkutė and her team grow this crystal in the Optoelectronic Technology Laboratory at FTMC.
(Just above the scientist's thumb, we can see a tiny "dot" - it holds 15 quantum superlattices. Photo: FTMC)
In simple terms, superlattices consist of tiny semiconductor layers - quantum wells and very narrow barriers between these wells. "In this way, due to quantum-mechanical effects, an electron entering the well can pass through the barrier. This is called 'quantum tunnelling'.
Because the barriers are so thin, the phenomenon known as 'miniband' occurs. There is a lot to explain and read about this, but the most important thing is that the miniband is what produces the wave amplification effect," says FTMC PhD student.
V. Čižas and his colleagues have published a paper on this research in the prestigious physics journal Physical Review Letters. FTMC research team is now working to attract the interest of scientific institutions and businesses around the world to their invention.
Written by Simonas Bendžius
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