In this work, we measure the thermal and thermoelectric properties of large-area Si_0.8Ge_0.2 nano-meshed films fabricated by DC sputtering of Si_0.8Ge_0.2 on highly ordered porous alumina matrices. The Si_0.8Ge_0.2 film replicated the porous alumina structure resulting in nano-meshed films. Very good control of the nanomesh geometrical features (pore diameter, pitch, neck) was achieved through the alumina template, with pore diameters ranging from 294 ± 5nm down to 31 ± 4 nm. The method we developed is able to provide large areas of nano-meshes in a simple and reproducible way, being easily scalable for industrial applications. Most importantly, the thermal conductivity of the films was reduced as the diameter of the porous became smaller to values that varied from κ = 1.54 ± 0.27 W K⁻¹m⁻¹, down to the ultra-low κ = 0.55 ± 0.10 W K⁻¹m⁻¹ value. The latter is well below the amorphous limit, while the Seebeck coefficient and electrical conductivity of the material were retained. These properties, together with our large area fabrication approach, can provide an important route towards achieving high conversion efficiency, large area, and high scalable thermoelectric materials.

Scandium nitride (ScN) is an emerging indirect bandgap rocksalt semiconductor that has attracted significant attention in recent years for its potential applications in thermoelectric energy conversion devices, as a semiconducting component in epitaxial metal/semiconductor superlattices and as a substrate material for high quality GaN growth. Due to the presence of oxygen impurities and native defects such as nitrogen vacancies, sputter-deposited ScN thin-films are highly degenerate n-type semiconductors with carrier concentrations in the (1–6) $\times$ 10²⁰ cm⁻³ range. In this letter, we show that magnesium nitride (Mg_xN_y) acts as an efficient hole dopant in ScN and reduces the n-type carrier concentration, turning ScN into a p-type semiconductor at high doping levels. Employing a combination of high-resolution X-ray diffraction, transmission electron microscopy, and room temperature optical and temperature dependent electrical measurements, we demonstrate that p-type Sc_1-xMg_xN thin-film alloys (a) are substitutional solid solutions without Mg_xN_y precipitation, phase segregation, or secondary phase formation within the studied compositional region, (b) exhibit a maximum hole-concentration of 2.2 $\times$ 10²⁰ cm⁻³ and a hole mobility of 21 cm²/Vs, (c) do not show any defect states inside the direct gap of ScN, thus retaining their basic electronic structure, and (d) exhibit alloy scattering dominating hole conduction at high temperatures. These results demonstrate Mg_xN_y doped p-type ScN and compare well with our previous reports on p-type ScN with manganese nitride (Mn_xN_y) doping.

This work discusses measurement of thermal conductivity (k) of films using a scanning hot probe method in the 3ω mode and investigates the calibration of thermal contact parameters, specifically the thermal contact resistance (R^th _C) and thermal exchange radius (b) using reference samples with different thermal conductivities. R^th _C and b were found to have constant values (with b = 2.8 ± 0.3 μm and R^th _c = 44 927 ± 7820 K W⁻¹) for samples with thermal conductivity values ranging from 0.36 W K⁻¹ m⁻¹ to 1.1 W K⁻¹ m⁻¹. An independent strategy for the calibration of contact parameters was developed and validated for samples in this range of thermal conductivity, using a reference sample with a previously measured Seebeck coefficient and thermal conductivity. The results were found to agree with the calibration performed using multiple samples of known thermal conductivity between 0.36 and 1.1 W K⁻¹ m⁻¹. However, for samples in the range between 16.2 W K⁻¹ m⁻¹ and 53.7 W K⁻¹ m⁻¹, calibration experiments showed the contact parameters to have considerably different values: R^th _c = 40 191 ± 1532 K W⁻¹ and b = 428 ± 24 nm. Finally, this work demonstrates that using these calibration procedures, measurements of both highly conductive and thermally insulating films on substrates can be performed, as the measured values obtained were within 1–20% (for low k) and 5–31% (for high k) of independent measurements and/or literature reports. Thermal conductivity results are presented for a SiGe film on a glass substrate, Te film on a glass substrate, polymer films (doped with Fe nano-particles and undoped) on a glass substrate, and Au film on a Si substrate.