arXiv subjects

Astrid D. Kengne

Publications and source records attributed to Astrid D. Kengne.

2 recordsLinked to original sources

arXiv2026

Enabling the Ambient Pressure Growth of ScB2 Crystals for AlGaN Power Electronics

Here we report the growth of single crystalline ScB2, an ultrahigh-temperature ceramic, at ambient pressure in a laser-heated Optical Floating Zone via the travelling solvent method. Crystals have been grown from both Sc-rich (55-65 at% Sc) and B-rich self-flux (80-83 at% B) at growth rates in the range of 0.2-2 mm/hr. The structure of grown crystals is in good agreement with an AlB2-type layered hexagonal phase, space group P6/mmm, with lattice constants a = 3.1423(2) Å (resp. 3.1502(3) Å) and c = 3.5084(3) Å (resp. 3.5041(3) Å) for crystals grown under Sc-rich (resp. B-rich) conditions. Crystals natively grow along the in-plane [100] direction. Electron backscattered diffraction shows that Sc-flux growth results in boules with multiple domains containing Sc inclusions, with the domains highly aligned. In contrast, B-flux boules are single domain after the initial nucleation region. Rocking-curve measurements of B-flux crystals for the (h000) and (000l) reflections show single peaks, establishing that the crystals are free from grain boundaries; the asymmetry in the scattered-intensity tails suggests the presence of point defects. Surface X-ray photoemission spectroscopy shows that the electronic environment in B-flux crystals is superior to that of Sc-flux crystals and produces highly resolved binding-energy peaks for B 1s and Sc 2p. Work-function measurements for the (11-20) plane give a value of approximately 5 eV, consistent with the highly electrically conductive nature of ScB2. These results demonstrate the viable ambient-pressure growth of ScB2, establish it as a lattice-matched substrate candidate for Al-rich AlGaN power microelectronics, and show that this growth route enables scalable manufacturing of ScB2 substrates.

cond-mat.mtrl-sci↗

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↗