Tailoring thermal conductivity by engineering compositional gradients in Si_sub1−xsub_ Ge _subxsub_ superlattices
Pablo Ferrando-Villalba, Aitor F. Lopeandía , Francesc Xavier Alvarez , Biplab Paul, Carla de Tomás, Maria Isabel Alonso, Miquel Garriga, Alejandro R. Goñi, Jose Santiso, Gemma Garcia, Javier Rodriguez-Viejo, Issue 9,
The transport properties of artificially engineered superlattices (SLs) can be tailored by incorporating a high density of interfaces in them. Specifically, SiGe SLs with low thermal conductivity values have great potential for thermoelectric generation and nano-cooling of Si-based devices. Here, we present a novel approach for customizing thermal transport across nanostructures by fabricating Si/Si1−x Ge x SLs with well-defined compositional gradients across the SiGe layer from x = 0 to 0.60. We demonstrate that the spatial inhomogeneity of the structure has a remarkable effect on the heat-flow propagation, reducing the thermal conductivity to ∼2.2 W·m−1·K−1, which is significantly less than the values achieved previously with non-optimized long-period SLs. This approach offers further possibilities for future applications in thermoelectricity.