For harvesting energy from waste heat, the power generation densities and fabrication costs of thermoelectric generators (TEGs) are considered more important than their conversion efficiency because waste heat energy is essentially obtained free of charge. In this study, we propose a miniaturized planar Si-nanowire micro-thermoelectric generator (SiNW-μTEG) architecture, which could be simply fabricated using the complementary metal–oxide–semiconductor–compatible process. Compared with the conventional nanowire μTEGs, this SiNW-μTEG features the use of an exuded thermal field for power generation. Thus, there is no need to etch away the substrate to form suspended SiNWs, which leads to a low fabrication cost and well-protected SiNWs. We experimentally demonstrate that the power generation density of the SiNW-μTEGs was enhanced by four orders of magnitude when the SiNWs were shortened from 280 to 8 μm. Furthermore, we reduced the parasitic thermal resistance, which becomes significant in the shortened SiNW-μTEGs, by optimizing the fabrication process of AlN films as a thermally conductive layer. As a result, the power generation density of the SiNW-μTEGs was enhanced by an order of magnitude for reactive sputtering as compared to non-reactive sputtering process. A power density of 27.9 nW/cm2 has been achieved. By measuring the thermal conductivities of the two AlN films, we found that the reduction in the parasitic thermal resistance was caused by an increase in the thermal conductivity of the AlN film and a decrease in the thermal boundary resistance.

GeSn is being paid much attention as a next-generation channel material. In this work, we performed the excitation of forbidden transverse optical (TO) phonons from strained GeSn, as well as longitudinal optical (LO) phonons, under the backscattering geometry from the (001) surface by oil-immersion Raman spectroscopy. Using the obtained LO/TO phonons, we derived the phonon deformation potentials (PDPs), which play an important role in the stress evaluation, of the strained Ge1− x Sn x for the first time. The results suggest that PDPs are almost constant for the Ge1− x Sn x (x < 0.032). Biaxial stress calculated using the derived PDPs reasonably indicated the isotropic states.

Si1-x Ge x is one of the prospective materials for the next-generation transistors due to its high carrier mobility, especially for high Ge concentration Si1-x Ge x . Inducing strain in the Si1-x Ge x leads to transistor performance improvement, however it is difficult to evaluate strain induced in the channel region because the strained Si1-x Ge x channel may be scaled down to nanosize and relaxed complicatedly. We adopted oil-immersion Raman spectroscopy to evaluate the stress in the Si1-x Ge x nanostructure. In this technique, the anisotropic biaxial stress state in the Si1-x Ge x nanostructure can be evaluated. As a result, the nanostructure size dependence of the biaxial stress states in the Si1-x Ge x mesa structure on the Ge substrates was obtained, which was confirmed for the Si1-x Ge x with 76, 85, 92% Ge concentrations.

We report on an anomalous mode distinct from both optical and acoustic modes in phonon dispersion curves of bulk Si1−xGex alloy with x taking the values of 0.16, 0.32, 0.45, and 0.72. The anomalous mode at approximately 13 meV was observed directly using inelastic x-ray scattering along the Γ–X ([00q]) direction. The phonon dispersion relations of the anomalous mode indicate that there was no momentum dependence, similar to those of the longitudinal and transverse optical modes (Ge–Ge, Si–Ge, and Si–Si modes). In contrast to the acoustic and optical phonon modes, the energy of the anomalous mode shows no Ge fraction dependence. The molecular dynamics simulation corroborates that the Ge–Ge pairs or Ge atom clusters, which are surrounded by Si atoms, provide the anomalous mode, which is unique to the alloy structure. It has been suggested that such a localized vibration mode with no propagation significantly affects the acoustic modes, leading to low thermal conductivity in the SiGe alloy.

The strain-free Raman shift of the Ge–Ge mode, , of Ge-rich Si1−xGex (x: Ge fraction) was determined accurately from the bulk Ge-rich Si1−xGex samples fabricated by the Czochralski (Cz) method. Using the obtained , the phonon deformation potentials (PDPs), p and q, and the strain-shift coefficient bLO of isotropic biaxial strained Ge-rich Si1−xGex thin films were extracted by oil-immersion Raman spectroscopy using Raman peak shifts of longitudinal and transverse optical (LO and TO) phonon modes. As a result, it was confirmed that these parameters are almost constant with small variations and that the strain-shift coefficient bLO is in good agreement with ab initio calculations. The parameters determined in this work are essential to realize accurate strain measurements using Raman spectroscopy for Ge-rich Si1−xGex devices.