Improving the stability of SWIR-emitting InAs QDs with a ZnSe/ZnS multishell for soft optical sensors

Short-wave infrared (SWIR) light holds extraordinary potential for sensing and imaging due to its high optical transparency, eye safety and excellent ability to penetrate scattering media. Among the various quantum dot (QD) materials explored for SWIR emission, III-V QDs, particularly InAs, have emerged as promising candidates due to their narrow bandgap and their environmentally friendlier profile compared to conventional Cd- and Pb-based QDs, which are restricted under RoHS regulations because of their toxicity. Despite their promise, implementing InAs QDs in optoelectronic devices like soft sensing architectures, remains challenging. Achieving high optical performance while preserving structural and chemical stability is a critical issue, as bare InAs QDs suffer from severe surface defects and exhibit very low photoluminescence quantum yield (PLQY ≈ 1%). Surface passivation with wide-bandgap Cd-free semiconductors such as ZnSe and ZnS can improve optical properties; however, the significant lattice mismatch with InAs generates interfacial strain, typically limiting PLQY values to around 15% in the SWIR spectral range. To address these limitations, different ZnSe/ZnS multishell growth strategies were investigated. Introducing intermediate buffer layers such as a thin ZnSe or graded ZnxSeS1−x is expected to mitigate lattice mismatch and gradually relax interfacial strain between the InAs core and the outer ZnS shell. This approach may enable thicker shell growth while minimizing defect formation and improving nanocrystal stability. To efficiently explore the multidimensional synthetic parameter space and optimize the shelling process with fewer experimental iterations, a Design of Experiments (DoE) methodology was employed. Ultimately, optimized QDs are expected to enable integration into soft optical SWIR sensing systems.