Optical and structural properties of GeSn/SiGeSn multiple quantum wells for infrared optoelectronics

We have investigated the correlation between structural and defect properties, and the optical performance of GeSn/SiGeSn multi-quantum well (MQW) structures as a function of the number of QWs. Our results show that significant diffusion and intermixing occur at the GeSn/SiGeSn interfaces during the sample growth. The intermixing is more pronounced at larger depths below the surface where the Sn and Si composition profile in the QWs layers undergoes a transition from a block-shaped to a compositionally graded Lambda-shaped profile. Simultaneously, the peak Sn concentration in the QWs reduces with depth up to 2.0 +/- 0.2 at.% while the integrated photoluminescence (PL) is significantly degraded. The reduced PL emission from both the GeSn buffer and GeSn QWs is attributed to the increasing density of non-radiative recombination centers in the MQWs due to alloy disordering due to diffusion. The use of PL from the GeSn buffer layer as a reference is shown to be important to analyze PL from SiGeSn/GeSn QWs and more generally from (Si)GeSn materials.