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Dan Buca and his team are developing photonic components, such as lasers and sensors, that can be seamlessly integrated into silicon chips. The material consists solely of elements from the silicon group and can convert waste heat into electrical energy.
Photonic components offer a key advantage: compared to electronic components, they can transmit large volumes of data with exceptional energy efficiency. This is because they use light instead of electricity. Photonic components have numerous potential applications. These include optical sensors in self-driving cars that detect objects using light, as well as lasers that serve as signal generators in photonic circuits. The long-term goal is to integrate photonic components directly onto microchips.
However, there is a material challenge. Silicon – the foundation of modern information technology – reaches its limits in such applications. As an indirect semiconductor, this element from the fourth group of the periodic table can emit and absorb light only inefficiently. In other words, silicon is poorly suited for generating or detecting photons. Alternatives based on materials from other chemical groups, such as gallium arsenide, do exist. However, integrating these III–V semiconductors into conventional chip manufacturing is complex and expensive. In addition, the toxic element arsenic makes handling and disposal more difficult.
We are developing direct semiconductors based on elements from the fourth main group. They can be easily integrated into standard chip manufacturing processes.
“Researchers worldwide are therefore searching for efficient light-emitting materials that can be integrated directly into silicon technology. We are developing direct semiconductors based entirely on elements from the fourth group – the silicon group,” says Dr. Dan Buca from the Peter Grünberg Institute (PGI-9). “This means they can be easily integrated into standard chip manufacturing processes.” These new semiconductors are designed to emit and detect photons – a highly demanding task. However, after more than ten years of research, Buca’s team and its cooperation partners have made significant progress.
Energy saver
During their extensive investigations of new alloys for photonic applications, the Jülich scientists and their collaboration partners discovered another remarkable property: the material can convert heat into electricity, meaning it is thermoelectric. “Sometimes you find more than you were looking for,” explains Buca. “Embedded in silicon-based microchips, the germanium–tin compound could, in the future, convert their waste heat back into electrical energy. This type of energy harvesting would significantly reduce cooling requirements and electricity consumption,” explains Buca. Moreover, many of today’s most efficient thermoelectric materials contain lead, which is harmful to both the environment and human health.
2015 First optically pulsed laser: Buca’s team produces a germanium–tin compound that – when grown on an intermediate layer deposited on a silicon wafer – can amplify optical signals and generate pulses of infrared laser light. Crucial to this is ensuring that more than 8 % of the atoms in the compound are tin atoms, achieved through precise control of the manufacturing process. The breakthrough came from the precise tuning of the growth conditions.
2020 A continuous beam of light: Together with French cooperation partners, the researchers are developing a new variant of the germanium–tin laser. It emits a stable, continuous beam of light and, at low temperatures, approaches the performance of gallium arsenide lasers. One challenge remains, however: the laser must still be excited by light – a process known as optical pumping. As a result, it cannot yet convert electrical data signals directly into light and therefore does not fully meet the requirements for practical applications.
2021 Alloy also receives light: Together with partners from Italy, Buca’s team demonstrates that the germanium–tin alloys are also suitable for compact photodetectors. Their cost-effective sensor detects photons in the short-wave infrared (SWIR) region and – by simply reversing the bias voltage – in the near-infrared (NIR) region. This makes it possible, for example, to distinguish between liquids that look identical to the human eye. SWIR sensors are also suitable for use in vehicle cameras, as they can see through rain and haze more effectively than conventional visible-light cameras. Unlike visible light, SWIR is scattered less by water droplets.
2024 Electrically pumped laser: An international team led by Buca presents an electrically pumped semiconductor laser that emits continuous light and consists exclusively of elements from the silicon group. The laser requires only 5 milliamperes of current and less than 2 volts – comparable to the consumption of a light-emitting diode. It is based on a specially engineered structure composed of ultrathin layers of silicon–germanium–tin and germanium–tin. However, the laser operates only at temperatures of -180 °C, which limits its use in practical applications. A similar limitation once applied to optically pumped germanium–tin lasers, which now operate at room temperature.
What comes next?
Most recently, Buca’s team, in collaboration with research partners, succeeded in combining silicon, germanium, tin, and carbon into a single crystalline material – something that had long been considered virtually impossible due to the very different properties of the individual elements. With the exception of lead, all Group IV elements are abundant, recyclable, and non-toxic. This makes materials based on these elements particularly attractive in a world striving for greater sustainability.
The outlook is promising: building on earlier advances in Group IV semiconductors, the newly developed material offers even greater control over electronic and optical properties. This could enable improved lasers, photodetectors, thermoelectric materials, and future quantum devices that remain compatible with standard silicon chip technology. Initial investigations also suggest that the material could be used to create qubits, the computational units of quantum computers. However, research in this area is still in its infancy.
With funding from the EU, the German Research Foundation (DFG), and the German Federal Ministry of Research, Technology and Space, Buca and his team now aim to demonstrate that Group IV alloys are suitable materials for many functions in modern information technology. With the help of prototypes, the researchers hope to spark industry interest and pave the way for future commercial applications. Buca emphasizes, however, that the transition from proof of concept in the laboratory to industrial applications remains a major challenge: “This will not be possible without substantial financial resources and strong industry partnerships.”
The manufacturing process: The Jülich alloys are deposited at low temperatures onto industry-standard silicon wafers. They are produced through chemical reactions of gaseous compounds containing elements from the fourth group of the periodic table. The chemical vapour deposition (CVD) process takes place in a system comparable to those used in the semiconductor industry. The challenge is that incorporating up to four different elements into a single crystal structure creates mechanical strain that can lead to cracks, defects, or phase separation. This strain arises because the atoms differ significantly in size: tin atoms, for example, are around 20 % larger than silicon atoms and nearly 80 % larger than carbon atoms. In addition, the elements differ greatly in their bonding behaviour and chemical reactivity during crystal growth. Through years of experimental work, the Jülich researchers identified growth conditions under which these challenges can be overcome.
This text is taken from the 1/26 issue of effzett. Text: Frank Frick
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Last Modified: 13.08.2026