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Microstructuring makes GeSn semiconductor alloys stable at high temperature


Researchers led by the ESRF have found that by microstructuring GeSn semiconductor alloys, they are stable at higher temperatures than the unstructured material. Their results are published today in ACS Applied Materials and Interfaces.

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Light emission capability is a key element in a today’s microelectronics industry, as it is needed in optoelectronic devices like LEDs or lasers used in telecommunications and sensing applications. However, the microelectronics industry requires very specific materials to create photonic properties.

Today, silicon is the most used material in microelectronics, and it is often organised in wafers, which represent the base of multilayer devices. In order to have the desired functionalities and performances, silicon needs to “marry” with compatible elements.

In semiconductors, luminescence is crucial for the optoelectronic applications. Researchers differentiate those materials that are direct band material (with high luminescence) and those which are indirect band (with low or no luminescence). Silicon does not emit light efficiently because it is an indirect band material, so it requires that the elements placed on top of it are luminescent. The element germanium, when mixed with tin, becomes a direct band material and therefore emits light more efficiently. “GeSn alloy is fully compatible with silicon, and it is therefore very promising for the development of photonic devices”, explains Valentina Bonino, postdoc at ID16B and first author of the publication.

However, Ge-Sn alloys also present some drawbacks. During the annealing process of the alloy, where temperatures of 350 degrees Celsius or higher are reached, tin tends to segregate from the material and hence, it loses its luminescent properties. Now the team led by the ESRF have found a recipe to avoid the separation of the material: microstructuring.


Jaime Segura, scientist in charge of ID16B and co-author of the publication, places a sample in the Experimental hutch of the beamline. Credits: S. Candé.

The ESRF team, together with scientists from the CEA and the Université Grenoble Alpes, in France, created microdisks and microrods with a concentration of 16.9% of tin in the Ge-Sn layers. At ID16B, they studied the distribution of Ge and Sn in microstructures annealed at 400 degrees Celsius using X-ray fluorescence mapping with nanometer resolution. They observed that microstructures isolated the origin of the segregation in a single microstructure, keeping the rest “safe” from segregation. “Basically we go through the thermal processes at a smaller scale, so we can confine the origin of the separation of tin and limit it”, says Jaime Segura, scientist in charge of ID16B and corresponding author of the publication.

The results were quite unexpected. The concentration of tin and the surface area of the microstructures dictated whether the tin was going to separate or not. Thanks to these findings, it should be possible to find the maximum microstructure area needed to avoid segregation for a given tin concentration at a certain temperature, and this will enable the optimization of wafers during the fabrication of the devices. “The results bring important benefits to these alloys, as we can manage their defects and therefore improve optoelectronic applications where they are used”, concludes Segura.


Bonino, V., et al, ACS Applied Materials and Interfaces.

Text by Montserrat Capellas Espuny

Top image: One of the microdisks studied. Credits: Bonino, V. et al. ACS Applied Materials and Interfaces.