Scientists have been able to increase the power of semiconductor lasers using barrier layers that prevent electrons from leaking from the active zone of the device, where the radiation is generated. Such layers prevent charged particles from flying past at high speeds, as a result of which they accumulate and create a more powerful light pulse. The proposed approach will significantly increase the efficiency of existing lasers, diagnostic systems, and range measuring devices. The results of the study, supported by a grant from the Presidential Program of the Russian Science Foundation (RSF), were published in the Journal of Luminescence.
Russian scientists have figured out how to increase the power of semiconductor lasers. Devices emitting light with a wavelength of about 1550 nanometers in the infrared range are used to transmit information over long distances: tens, hundreds and thousands of kilometers, as well as in automotive lidars - devices for measuring ranges and obtaining 3D images of the surrounding space. They are also used in medical diagnostic systems and security-related applications.
These devices are created from multilayer crystalline materials - heterostructures - based on solid solutions of aluminum, gallium, indium and arsenic, since they are capable of emitting light in the required region of the infrared range. Heterostructures are designed in such a way that when voltage is applied through them, particles carrying electric charge begin to move in opposite directions. Conventionally, negatively charged electrons move from right to left, and positively charged quasiparticles called “holes” move in the opposite direction.
To create the most powerful laser possible, you need to make sure that all the electrons and “holes” fall into the active region and remain there. However, in practice, some particles "fly" past this zone - this process is called "leakage of charge carriers."
Specialists from the Physico-Technical Institute named after. A.F. Ioffe RAS (St. Petersburg) and the Polyus Research Institute named after. M.F. Stelmakh (Moscow) created heterostructures based on solid solutions of aluminum, gallium, indium and arsenic, in different parts of which barrier layers of a ternary compound of aluminum–indium–arsenic were placed. It is difficult for particles to pass through such barriers due to lack of energy, and as a result, the probability of particles being captured in the active region approaches 100%, and those that would flow past the active zone are practically not observed.
“We were able to identify the main cause of power loss in semiconductor lasers and eliminate it by introducing a barrier layer for electrons into the heterostructure. In the future, we plan to look for new options for the laser design itself, which will further increase the efficiency of the device,” said the project leader, Candidate of Physical and Mathematical Sciences, researcher at the Physico-Technical Institute. A.F. Ioffe RAS Alexander Podoskin.
The authors formed heterostructures in a specialized installation, where single-crystal layers of a given composition were sequentially deposited from molecules of high-purity compounds onto a substrate. In experiments, scientists examined samples with different numbers and locations of barriers: the first without barrier layers, the second with one such layer that prevents electrons from “flying” past the active zone, the third with the same layer, but in the path of “holes,” the fourth sample contained two barrier layers for both electrons and holes.
The authors then examined the radiation power of the resulting samples by applying an electric current of the same magnitude to them. The experiment showed that a heterostructure with one barrier layer for electrons has the greatest power. Its performance was twice as high as that of the original material without barrier layers. At the same time, an attempt to put a barrier in the way of the “holes” did not produce significant improvements.
This can be explained by the fact that electrons in the materials used by the authors are much more mobile particles, their speed of movement through the material is higher than that of “holes,” the authors of the experiment said. Accordingly, it is they who usually “fly” past the active zone, which makes the main contribution to the reduction in radiation power.
“It was unexpected for us that one barrier layer for electrons turned out to be more effective than two – for electrons and for “holes.” Therefore, we will also look for the reasons for this result,” noted Alexander Podoskin.
Increasing the power of semiconductor lasers by creating barrier layers that prevent electron leakage from the laser active zone is a major achievement, confirmed Ivan Ushakov, professor and head of the department of physics at NUST MISIS. “The overall characteristics of the laser systems being developed are significantly higher than the characteristics of existing analogues,” he said.In electronics, there is a continuous evolution of materials, both from the point of view of miniaturization and from the point of view of expanding useful properties, Dmitry Divakov, associate professor of the department of mathematical modeling and artificial intelligence of St. Petersburg Electrotechnical University "LETI", told Izvestia.
“Electronics technologies use a lot of substances harmful to the environment, many acidic and alkaline processes, various types of plastics and other high-molecular compounds, which are sometimes very difficult to dispose of. The structures presented by the team of authors are more environmentally friendly, which is also a significant advantage for electronic production,” the expert said.
Semiconductor lasers in the infrared range are in demand in many areas, and the achieved parameters of such lasers are impressive, for example, the radiation power density at the output end is several tens of megawatts per square centimeter in continuous mode, which seemed fantastic just a decade and a half ago, said Vladimir, professor of the Department of General Physics at MIPT Petukhov.
“We can say that, of course, there is an achievement that makes it possible to create more advanced heterostructures of semiconductor lasers, but it is not yet possible to assess the extent of its impact on the production of semiconductor lasers due to a lack of information,” he said.
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