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Researchers synthesized single-crystalline scandium diboride ($\text{ScB}_2$) at ambient pressure using a laser-heated optical floating zone via the traveling solvent method. Boron-rich self-flux conditions produced grain-boundary-free, single-domain boules oriented along the [100] direction with high electronic quality and a ~5 eV work function. This ambient-pressure route overcomes severe high-pressure fabrication bottlenecks to provide a viable, lattice-matched substrate for ultra-wide-bandgap Al-rich AlGaN power microelectronics.
High-efficiency AlGaN power electronics just secured a scalable manufacturing foundation: single-crystal $\text{ScB}_2$ substrates can now be synthesized at ambient pressure without grain boundaries.
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) \AA\ (resp. 3.1502(3) \AA) and c = 3.5084(3) \AA\ (resp. 3.5041(3) \AA) 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.