A new mechanism for forming nanocrystals for lasers has been introduced at St. Petersburg State University.

The research findings have been published in the high-ranking scientific journal Nanoscale Horizons. The InGaN alloy (indium-gallium nitride), currently utilized in power electronics and LEDs, also shows promise for gas sensors, solar cells, and hydrogen cells. Its widespread application is limited due to the challenges in synthesizing a stable layer.

Recently, scientists from St. Petersburg University thoroughly studied the mechanisms behind the formation of three-dimensional (non-planar) structures based on InGaN material, applying scientific and systematic approaches to describe the growth processes of these structures. Prototypes of LEDs, gas sensors, water-splitting cells, and more are already being developed at SPbU based on such compounds.

As physicists point out, in the familiar "planar" form known to the scientific community, complex microelectronic structures are created on a flat surface through several sequential stages of material deposition, etching, and lithography to form various layers and components of the device. However, in the case of InGaN, it is not possible to form such "flat" structures using classical methods.

Due to the solubility gap effect, the production of InGaN layers with a high indium (In) content leads to the decomposition of this material into separate phases and the formation of a significant number of defects. The mismatch of the lattice constants of these materials also contributes to the formation of defects. All of this significantly reduces the performance of devices that utilize these structures.

Physicists at St. Petersburg University have discovered a new mechanism for the formation of nanocrystals based on InGaN directly on the surface of silicon.

“In particular, we have explained for the first time a new mechanism for the formation of InGaN nanowire nanocrystals that possess a spontaneously formed 'core-shell' structure. Experimental research results showed that the indium content in the core of the nanocrystal can be around 40 percent or more, while in the shell it is about four percent. It is important to note that achieving such a high indium content in high-quality InGaN layers is extremely challenging, but we succeeded,” said the project lead, Rodion Reznik, head of the laboratory of new semiconductor materials for quantum informatics and telecommunications at SPbU.

Increasing the indium content in InGaN leads to a change in the wavelength (in other words, a change in the color of the emission) from such nanostructures, significantly expanding the potential for applying this material in the creation of new efficient LEDs, lasers, solar cells, and much more. The intense emission from the nanostructures produced by the researchers indicates the high optical quality of the new material.

“The results of theoretical research have shown for the first time that the formation of 'core-shell' heterostructures in non-catalytic InGaN nanowire nanocrystals is associated with periodic changes in growth conditions at the top of such nanostructures. It turned out that the ratio of III and V group atoms from the periodic table at the top changes even during the growth of a single monolayer of such a nanostructure,” explained Rodion Reznik, head of the laboratory of new semiconductor materials for quantum informatics and telecommunications at SPbU.

According to the physicist, at the initial stage of nanocrystal growth, the conditions are balanced, allowing the solubility gap effect to be overcome and enabling the formation of an indium-enriched core of the nanocrystal. Then, the conditions shift to those enriched with the III group, and the mechanism of shell formation changes. At this stage, the shell can be effectively removed using chemical methods without degrading the quality of the core.

It should be noted that the staff of the laboratory of new semiconductor materials for quantum informatics and telecommunications at SPbU are engaged in studying new materials for microelectronics: single-photon sources, efficient LEDs, solar cells, lasers, nanopiezo generators, and also integrating them with a silicon platform. All these achievements are a continuation of efforts to enhance quantum technologies for microelectronics, initiated by two Nobel laureates: SPbU alumnus, Nobel Prize winner in Chemistry Alexey Ekimov, and the organizer and rector of SPbAU, Zhores Alferov. More about his work was discussed by Rodion Reznik in the SPbU podcast “Genrich Terahertz”.