arXiv subjects

Ethan Scott

Publications and source records attributed to Ethan Scott.

2 recordsLinked to original sources

arXiv2026

Scandium diboride: a semi-metallic, lattice, thermally matched substrate for vertical AlGaN power electronics

We report the properties of hexagonal (space group P6/mmm) scandium diboride ($\mathrm{ScB}_2$) single crystals grown by a laser diode floating zone method at growth rates of ~1mm/hr under B-rich conditions with (002) rocking curve widths $Δω$=38'' approaching the quality of commercial SiC/GaN substrates. Lattice expansion measurements reveal matching to $\mathrm{Al_{0.55}Ga_{0.45}N}$ with a coefficient of thermal expansion ~5ppm/K at typical AlGaN growth temperatures, enabling thick AlGaN layers for ultra-wide bandgap (UWBG) power electronics >1kV. We measure semi-metallic room temperature resistivity ~15$μΩ$ cm, climbing to ~93$μΩ$ cm at 773K with a $T^2$ dependence effectively eliminating substrate parasitic resistance, the limiting factor in exploiting the full potential of UWBG. The Debye temperature $θ_{D,ScB_2}$ from heat capacity and lattice expansion is ~850K well matched to $θ_{D,ScB_2}$, but lower than the 1100K measured for Sc-rich growth conditions. We discuss Debye matching as a key substrate codesign criterion providing significant overlap in phonon modes for heat removal and thermal matching during AlGaN growth. The competitive thermal conductivity at room temperature 53W/mK is half that from full first principles calculations, a discrepancy we attribute to the presence of Sc-vacancies generated by B-rich growth. while the resistivity is ~2x the theoretical value, indicating that both electrons and phonons play equal role in thermal transport. The smooth ~2.5nm rms roughness surface enables advanced heat removal modalities through engineered phonon bridges and phonon polaritons in $\mathrm{ScB}_2$/AlGaN interfacial heterostructures, potentially allowing ~10-100x increase in power handling over state-of-the-art GaN/SiC.

cond-mat.mtrl-sci↗

arXiv2026

Closing the ultrahigh temperature metrology gap: non-contact thermal conductivity ($\mathrm{k}$) and spectral emittance ($\mathrm{\varepsilon_λ}$) of molybdenum up to 3200 K

Advances in next-generation hypersonic hot structures, high heat-flux fusion or fission components, and laser based additive manufacturing depend on reliable solid state thermal conductivity data at high and ultrahigh temperatures, where conventional measurements become increasingly sensitive to contact resistances, uncertain boundary conditions, and nonlinear radiative losses. Building on our initial demonstration of ultrahigh temperature steady-state temperature differential radiometry (SSTDR), we present a substantially more robust platform aimed at making high temperature thermal and radiative property measurements more routine. The method integrates lock-in infrared thermography with a spatially localized, modulated perturbation laser to form a conduction dominant differential observable along with hyperspectral pyrometry and a validated 2D axisymmetric steady state heat transfer model. Using high purity molybdenum as a benchmark, we report solid state thermal conductivity k(T) from 1500 - 3000 K (to the onset of melting) with uncertainties of 7.9-11 % enabled by comprehensive uncertainty propagation, sensitivity analysis, and bounding studies. We additionally provide normal spectral emittance of molybdenum in both solid and liquid states over 500-1000 nm. These advances establish SSTDR as an accurate, non-contact route for closing the high temperature k(T) data gap while simultaneously producing much needed phase dependent radiative property data for melt adjacent and extreme heat-flux applications. Note: This is a shortened abstract; full version in manuscript.

cond-mat.mtrl-sci↗