Optical constants and interband transitions of Ge1−xSnx alloys (x<0.2) grown on Si by UHV-CVD

Abstract The development of manufacturable direct band gap materials on Si is crucial for optoelectronic devices integrated with silicon circuits. Ge–Sn alloys with varying metastable compositions ranging from 2 to 20% were grown by UHV-CVD using a deuterium-stabilized Sn hydride with digermane. We use deep ultraviolet spectroscopic ellipsometry (0.74 to 6.6 eV) to determine the optical properties of this new class of Si-based infrared semiconductors in the Ge 1− x Sn x system. Optical analysis of the energy-derivatives in comparison with analytical lineshapes shows that the E 1 and E 2 interband transition energies decrease significantly with increasing Sn content. Tunability of these high-energy gaps shows promise for a direct E 0 band gap in this materials system.