ELEctrically pumped GermANium Tin lasEr on silicon – ELEGANTE

The objective of the ELEGANTE project is to demonstrate a laser source with germanium tin alloys, operating under electrical injection up to room temperature. Such a laser source made from group IV elements with a direct band gap would be a game-changer for silicon photonics and the development of photonic integrated circuits.
A monolithically integrated source on silicon substrate still represents a major challenge for silicon photonics and for More than Moore applications. The biggest bottleneck in this situation is the indirect nature of the band gap of silicon and germanium. This indirect band gap prevents one from obtaining optical gain at current densities compatible with integration. Laser emission on silicon chips has, therefore, relied on the use of intrinsically direct band gap III-V semiconductors that are coupled to a silicon photonics platform either externally, or through, die or wafer bonding followed by processing. This hybrid approach increases the complexity of fabrication as it requires processing of both III-V and silicon. On the contrary, a monolithically integrated optical source made from group IV elements would be fully CMOS compatible both in terms of materials and processes and could be a real game-changer for the architecture, design and ultimately production cost of silicon photonics.
The best option to achieve a group IV laser with performances compatible with integration is to use direct band gap semiconductors. Direct band gap can be obtained by strain engineering, by alloying germanium with tin, or by a combination of both. In this project, we will fabricate direct band gap germanium tin alloys on silicon substrates and demonstrate lasing under electrical injection with these structures with the objective to achieve lasing up to room temperature. Such a demonstration has not been reported so far, as only lasing at low temperature under optical pumping has been evidenced. We have already started working on the project and demonstrated a first optically pumped GeSn laser at the beginning of 2017, a clear indicator of the bright perspectives for this proposal. We expect to outperform the current state of the art, with a target of 10 kA cm-2 for threshold, by using quantum well heterostructures instead of bulk materials, electrical injection instead of optical pumping, strain engineering strategies to lower the tin content required to obtain direct band gap and sufficiently large energy difference between conduction valleys, and larger non-radiative lifetimes through material optimization. The fabricated lasers will be fully characterized using pulsed and continuous wave pumping from low temperature to room temperature, as lasing at low temperature is easier to achieve. We will evaluate the potential of these lasers that are expected to emit in the 1.7–4 µm spectral range for datacom and sensing applications. We will propose strategies compatible with the process flow of our industrial partner (STMicroelectronics) to integrate such lasers on silicon photonics integrated circuits.
This proposal gathers the main partners involved in France on the development of group IV optical sources. We further plan to develop for the first time in France the growth and processing of germanium tin alloys and be suppliers of high quality materials grown by chemical vapor deposition. This topic is highly competitive, considering the numerous groups involved in the developments of group IV lasers and the number of symposia devoted to this area. Funding from the ANR will help to launch this new activity at the French level, strengthen the partnerships between the groups involved in the project and will help all partners to remain at the forefront research in this area. The question whether a group IV laser can be competitive is also of tremendous importance for the industrial partner and his roadmap for silicon photonics development.