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2024: Laser emitters based on semiconductor nanostructures created in Russia
An employee of the Polyus Research Institute named after M.F. Stelmakh Holding "Schwabe" State Corporation Rostec has developed a technology for producing semiconductor nanostructures, and has also created powerful new generation laser emitters on their basis. This was reported to TAdviser on February 19, 2024 by representatives of Schwabe. The results of scientific work can be used in the production of medical equipment, unmanned vehicles, lidar systems and other devices. Read more here.
2020: MIPT solved the problem of generating far-infrared laser radiation in semiconductor structures
On January 30, 2020, it became known that physicists from the Moscow Institute of Physics and Technology and the Institute of Microstructure Physics of the Russian Academy of Sciences managed to solve the problem of generating far-infrared laser radiation in semiconductor structures. The key to her decision was the use of quantum pits of cadmium-mercury telluride. These compounds have long been known in photonics and electronics, however their key feature for laser applications remained undisclosed. The work is published in the journal ACS Photonics.
In a semiconductor diode laser, radiation occurs during the mutual destruction of conduction electrons and holes - vacant places on filled electronic orbitals. This process is called radiative recombination. However, light emission from electron and hole recombination is not the only possible outcome. Along with the emission of the photon, the released energy can go to the oscillation of the crystal lattice. But the most critical recombination process is one where the energy of the electron-hole pair immediately goes to heat other electrons, instead of useful light generation. Such a process of "wasting" electron-hole pairs in heat is called auger recombination - in honor of the French physicist Pierre Auger, who first studied this effect.
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The speed of the destructive auger process increases dramatically in semiconductors with a small energy distance between the levels of electrons and holes (in scientific terms, with a small band gap). We can say that the closer to each other the electron and the hole (on the energy scale), the stronger their desire for mutual annihilation with the release of heat. However, semiconductors with precisely a small band gap are required to create far-infrared lasers emitting at wavelengths of tens of microns. And it is these lasers that are in demand in the research of biological objects and the tasks of gas spectroscopy, noted in MIPT.
Amplification of non-radiative auger recombination and a decrease in the efficiency of a semiconductor laser with an increase in wavelength, however, are not laws of nature, but follow only from experience. There is no fundamental prohibition on the creation of a semiconductor structure that emits in the far infrared and is not subject to the auger process. Moreover, the requirements for the spectrum of electrons and holes, which ensures the complete prohibition of non-radiative recombination, are known from the work of Paul Dirac on electrons and positrons. Namely, electrons and holes must have the same mass at low energies and behave like massless particles - at large ones. But all attempts to translate these ideas into real material failed.
Researchers from MIPT and the Institute of Microstructure Physics of the Russian Academy of Sciences in Nizhny Novgorod found that electrons and holes have the properties necessary for laser applications in quantum pits of cadmium-mercury telluride. This material has a long history: it has been used for more than half a century to create thermal imagers, and about a decade ago it caused a boom in topological physics due to the special properties of electrons at its edges.
 | "For a long time, the laser prospects of cadmium-mercury telluride did not cause much enthusiasm, and no one paid attention to the" Dirac "form of the electron-hole spectrum. Laser physicists of the twentieth century worked with wide quantum pits with a large content of cadmium - this is far from the optimal composition, according to our calculations - therefore the desired phenomenon was not discovered. When the technology of the XXI century made it possible to grow narrow quantum pits, the field was filled with topological physicists, whose attention was focused on edge electrons. What is happening in the plane of the pit, and not on its edge, remained without due attention. And only our group managed to detect the desired suppression of auger recombination in narrow quantum wells, " noted Dmitry Svintsov, co-author of the study, head of the laboratory of optoelectronics of two-dimensional materials at MIPT |  |
As of January 2020, experiments on mercury telluride quantum pits grown at the Institute of Semiconductor Physics of the Russian Academy of Sciences (Novosibirsk) have already confirmed the possibility of laser generation with a wavelength of up to 20 microns. And the calculations of the "residual" recombination processes performed in the work show that this is not the limit, and the wavelength of radiation can be increased to 50 microns. The wavelength range of 30 to 50 microns is the most "forbidden" for existing semiconductor lasers based on elements of the III and V groups of the Mendeleev table due to strong self-absorption. But this negative effect - as well as auger recombination - is greatly weakened in mercury telluride, this time due to the large mass of atoms that make up the crystal lattice. Thus, the studied quantum wells have every prospect of closing the last "white spots" on the scale of electromagnetic radiation.
| | "Naturally, in the field of laser technology, mercury telluride quantum pits have competitors. The most serious are quantum cascade gallium arsenide lasers. They do not use electron-hole recombination, but are based solely on electronic transitions. Such a "paradigm shift" requires a very complex laser design and, as a result, a huge price - one cascade laser costs more than 6 thousand dollars. Mercury telluride allows you to extend the performance of an established, extremely simple and cheap laser diode design up to the far infrared range, " noted Dmitry Svintsov, co-author of the study, head of the laboratory of optoelectronics of two-dimensional materials at MIPT | |
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