MIPT and FIAN: Technology for improving the quality of semiconductor heterostructures

Main article: Semiconductor materials

2024: Russian scientists proposed to eliminate semiconductor defects using hypersonic

A team of researchers from MIPT and FIAN has developed an approach that in the future will allow, without direct contact with a semiconductor, to cure some types of defects in it. Scientists demonstrated the ability to "expel" a defect from a semiconductor structure using laser hypersonic, and the movement of the defect was detected by subtle changes in the structure of the spatial glow of the crystal. The study will help in the development of a simple and affordable technology for optimizing the quality of semiconductor heterostructures. The work is published in the Journal of Applied Physics. This was announced on January 18, 2024 by representatives of the Moscow Institute of Physics and Technology.

As reported, modern physics of semiconductor heterostructures studies complex multilayer objects with a cunning structure. For example, structures with multiple quantum wells for making lasers or photodetectors. Such structures may have pest defects - dislocations: atomic chains or even entire planes of atoms that are out of place. "Order breakers" appear in the crystal production process due to the heterogeneity of the substrate on which the structure is grown, accidental contamination, or insufficiently accurate control of certain process parameters.

Even at the current level of development of semiconductor technologies, it is impossible to perfectly control the production process at the atomic level. For example, in a large-format photosensitive matrix, in which many different heterostructural pixels are made using complex technology, 100% of pixels are not "healthy." Pest defects can lead to unpredictable changes in material properties. This leads to the appearance of incorrectly working, "sick" pixels. Accordingly, a method of affecting these pixels is needed in order to reduce their number if possible.

Previously, a mechanism has already been discovered for influencing one of the common types of linear defects using a beam of high-energy electrons: in a transmission electron microscope, dislocation can be detected, then using a focused beam of electrons to shift this dislocation or change its internal structure. Under certain conditions, it was possible to completely eliminate the structural defect. The idea of ​ ​ scientists from MIPT and FIAN was to implement a similar technique, but in a simpler, fully optical installation. As a method of exposure, they chose a focused laser pulse hundreds of picoseconds long. This pulse is absorbed in the near-surface layers crystal and disrupts the peace of the electron hole system, the main "inhabitants" of the semiconductor. To calm down, the system sheds energy in the form of phonons - quanta of oscillations of the crystal lattice. With the correct excitation mechanism, along with quasi-thermal phonons, a hypersonic deformation wave is formed, or, in another way, a pulse of coherent phonons of gigahertz or sub-terahertz frequencies. This wave, according to the authors, leads to the sliding of the defect and theoretically can allow "expelling" dislocations from the crystal. The scientists took a CdTe cadmium telluride single crystal film containing dislocations and exposed it to pulsed laser radiation at helium temperatures.

Then it was necessary to check that the pest defect had moved to another place. The optical microscope does not directly see the dislocation, it is too small. Physicists have connected an indirect method to solving the problem - microfotoluminescence at low temperature. Electron-hole pairs cling to defects in the crystal and, if the temperature is low enough, form bright point emitters. And when the defect moves around the crystal, the illumination pattern changed, and thus they caught the movement of dislocation.

source = FIAN

We have a tool that triggers a wave of hypersonic, which in turn stimulates the movement of the dislocation, and a tool that allows you to see its movement. Using the example of a common model semiconductor, we showed that you can choose the parameters of the tools and make the defect move. The method can be generalized to other semiconductor materials and tried to create technology. commented Vladimir Krivobok, head of the laboratory of optics of ultra-cold nuclear systems and functional materials of MIPT

Like many interesting scientific results, this one was obtained by side, in the process of studying complex semiconductor heterostructures. The idea allowed scientists to have two installations: a hypersonic microscope and a microfotoluminescence measurement system at low temperatures. A hypersonic microscope allows for a pulse that drives dislocation out of the semiconductor's crystal structure, and microphotoluminescence helps verify that the "therapy" has worked.

The results will be the basis for the development of a fully optical technology for local laser processing of extended defects in semiconductors. The study was carried out with the support of the Federal Academic Program Priority 2030 leadership.