Comparative study of rapid thermal and microwave annealing on the photoluminescence of compressively-strained GeSn alloys on Si

Group-IV GeSn alloys have gained significant attention as an attractive material system for silicon photonics. Thermal annealing provides an efficient route to improve the crystalline quality and overall performance of GeSn layers. Here, we present a comparative study on the effects of rapid thermal annealing (RTA) and microwave annealing (MWA) on GeSn samples grown on Si via Ge buffer layers containing ∼6.3% Sn under a compressive strain of 0.793%. Structural analysis reveals that RTA at ∼380 °C yields a modest strain relaxation of ∼20% and enhanced crystallinity. However, RTA at higher temperatures results in defect generation and a decrease in photoluminescence (PL) emission intensity. In contrast, MWA at a moderate power of ∼900 W achieves a higher strain relaxation of ∼27–28% while preserving both material quality and PL emission. This advantage is attributed to the more localized energy delivery and reduced thermal budget of MWA, which mitigates Sn diffusion and maintains alloy integrity. In addition, theoretical analysis of the strain-dependent band structure and spontaneous emission in GeSn further confirms that increased strain relaxation enhances the direct-gap character and radiative recombination. These findings demonstrate that MWA offers a more robust and scalable post-growth annealing route for optimizing GeSn layers while balancing strain engineering, optical performance, and material stability, thereby advancing the development of high-performance, complementary metal oxide semiconductor-compatible GeSn-based photonic devices.