Scandium diboride: a semi-metallic, lattice, thermally matched substrate for vertical AlGaN power electronics
Abstract
We report the properties of hexagonal (space group P6/mmm) scandium diboride (ScB2) 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 Al0.55Ga0.45N 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 ~15μΩ cm, climbing to ~93μΩ cm at 773K with a T2 dependence effectively eliminating substrate parasitic resistance, the limiting factor in exploiting the full potential of UWBG. The Debye temperature θD,ScB2 from heat capacity and lattice expansion is ~850K well matched to θD,ScB2, 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 ScB2/AlGaN interfacial heterostructures, potentially allowing ~10-100x increase in power handling over state-of-the-art GaN/SiC.
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BibTeX
@misc{chandrashekhar2026scandium,
title = {{Scandium diboride: a semi-metallic, lattice, thermally matched substrate for vertical AlGaN power electronics}},
author = {MVS Chandrashekhar and Daniel Joel Harrison and Ahamed Raihan and Astrid D. Kengne and R. Shipra and Han Xie and Tasnia Jabin and Monte Hendrix and Ethan Scott and Roshan S. Annam and Sharad Mahatara and Evan N. Crites and Allana G. Iwanicki and Luke J. Meiler and Maxime Siegler and Renae N. Gannon and Steven R Spurgeon and Ashutosh Giri and Rajeswari Kolagani and Joshua A. Burrow and Stephan Lany and Patrick Hopkins and Tyrel M. McQueen and Michael Spencer and Satya Khushwaha},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.24856},
eprint = {2609.24856},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.24856},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - Scandium diboride: a semi-metallic, lattice, thermally matched substrate for vertical AlGaN power electronics
AU - MVS Chandrashekhar
AU - Daniel Joel Harrison
AU - Ahamed Raihan
AU - Astrid D. Kengne
AU - R. Shipra
AU - Han Xie
AU - Tasnia Jabin
AU - Monte Hendrix
AU - Ethan Scott
AU - Roshan S. Annam
AU - Sharad Mahatara
AU - Evan N. Crites
AU - Allana G. Iwanicki
AU - Luke J. Meiler
AU - Maxime Siegler
AU - Renae N. Gannon
AU - Steven R Spurgeon
AU - Ashutosh Giri
AU - Rajeswari Kolagani
AU - Joshua A. Burrow
AU - Stephan Lany
AU - Patrick Hopkins
AU - Tyrel M. McQueen
AU - Michael Spencer
AU - Satya Khushwaha
PY - 2026
DA - 2026/09/21
PB - arXiv
DO - 10.48550/arxiv.2609.24856
UR - https://arxiv.org/abs/2609.24856
AB - We report the properties of hexagonal (space group P6/mmm) scandium diboride (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 Al_0.55Ga_0.45N 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 ~15μΩ cm, climbing to ~93μΩ 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 ScB_2/AlGaN interfacial heterostructures, potentially allowing ~10-100x increase in power handling over state-of-the-art GaN/SiC.
ER -