A team from the Technical University of Eindhoven (TU/e) and the Technical University of Munich (TUM) has succeeded in developing light-emitting, silicon-germanium alloys – something that was evading researchers for the past 50 years. As a result, the development of a silicon laser capable of integration into today’s chips is within reach for the first time.
“If we can implement on-chip and inter-chip electronic communications by optical means, speeds can be increased by a factor of up to 1,000,” said Professor Jonathan Finley, Professor of Semiconductor Quantum Nanosystems at TUM . “In addition, the direct combination of optics and electronics could drastically reduce the cost of chips for laser-based radar in self-driving cars, chemical sensors for medical diagnostics, and air and food quality measurements.”
Electronic chips produce heat when processing data and the solution could be in the field of photonics, since light pulses do not emit heat. The newly-developed alloys made of germanium and silicon are capable of emitting light. In a crucial step, these were produced with a hexagonal crystal lattice, see image below:
“This material has a direct band gap, and can therefore emit light itself,” said Finley.
Professor Erik Bakkers and his team at TU Eindhoven first produced hexagonal silicon back in 2015. They started by growing a hexagonal crystal structure with nanowires made of another material. This served as a template for a germanium-silicon shell on which the underlying material imposed its hexagonal crystal structure.
Initially, however, these structures could not be stimulated to emit light. Through the exchange of ideas with colleagues at the Walter Schottky Institute at the Technical University of Munich, who analysed the optical characteristics with each successive generation, the production process was finally optimised to a grade of perfection where the nanowires were indeed capable of emitting light.
“In the meantime, we have achieved properties almost comparable to indium phosphide or gallium arsenide,” said Bakkers. As a result, it appears to be just a matter of time before a laser made from germanium-silicon alloys and capable of integration into conventional production processes is developed.