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SiGeSn Laser for Silicon Photonics

Subject Area Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering
Term from 2016 to 2024
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 299480227
 
Final Report Year 2024

Final Report Abstract

The project target was the proof-of-concept of an electrically pumped group IV laser based on (Si)GeSn alloys. These alloys that include the binary GeSn and ternary SiGeSn semiconductors are epitaxially grown in standard large wafer size industry reactors in conventional Si-technology cleanroom infrastructure. The fact that the direct bandgap GeSn semiconductor is composed of all group-IV elements minimizes contamination issues and open the way to monolithic laser integration in CMOS electronic processes. At the onset of the project, the project partners had already experience in GeSn based heterostructure growth and characterization from previous activities on optically pumped lasers. At the project start, the state-of-the-art consisted in optically pumped bulk GeSn microdisk and waveguide lasers with thresholds of 100 kW/cm2 at a temperature of 10K and 2-3 MW/cm2 at 260K. For MQW heterostructures, laser emission was demonstrated up to 150K with the confinement effect bringing the laser threshold down to 30kW/cm2. Two approaches were followed to go beyond the state of the art, namely: 1. Grow the most promising structures for electrical pumping based on models calibrated by previous experimental results, conceive a fabrication flow for diodes including electrical injection and measure the results. 2. Further develop the heterostructure growth, including precursor change for epitaxy, and add strain engineering in the fabrication process. Both approached were successfully finished with the main results presented below: Reduction of electrically pumped Ge0.86Sn0.14 bulk laser thresholds below 50 mA. This laser shows a substantial improvement in threshold over another electrically pumped GeSn laser reported during the project duration. The results were published in ACS Photonics. The world’s first electrically pumped CW SiGeSn MQW laser. This laser is tunable from CW to ns pulses and has a record low threshold of only 4 mA. CW electrical pumping was shown for the first time ever in a Si-based material. The world’s first CW optically pumped strained GeSn laser. Tensile strain was introduced by layer transfer and then using SiN stressor layers. A very low Sn content alloy (5%) was transformed into a direct bandgap material by applying a large tensile strain of 1.5%. The laser shows lasing up to 60K in CW and 120K in pulsed mode. The laser threshold was reduced to the to the present world record of 1kW/cm2 in CW mode and 0.8 kW/cm2 in pulsed mode The result was published in Nature Photonics. Since room temperature CW lasing has been demonstrated with optical pumping and cryogenic CW lasing has been achieved with electrical pumping, the remaining challenge consists in achieving CW electrical pumping together with room temperature operation. This remains a challenge to be addressed in future work. Other than this last goal, that remains an outstanding future challenge, all the goals of this project and new benchmarks going significantly beyond the previous state of the art have been reached.

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