二硼化钪：用于垂直AlGaN功率电子器件的半金属、晶格及热匹配衬底

中文摘要 AI 辅助

我们报道了通过激光二极管浮区法在富硼条件下以约1毫米/小时的生长速率生长的六方（空间群P6/mmm）二硼化钪（$\mathrm{ScB}_2$）单晶的性质，其（002）摇摆曲线宽度$\Delta\omega$=38''，接近商用SiC/GaN衬底的质量。晶格膨胀测量显示，其与$\mathrm{Al_{0.55}Ga_{0.45}N}$匹配，在典型AlGaN生长温度下热膨胀系数约为5ppm/K，从而能够生长厚AlGaN层，用于超过1kV的超宽禁带（UWBG）功率电子器件。我们测量到室温下半金属电阻率约为15$\mu\Omega$ cm，在773K时升至约93$\mu\Omega$ cm，并呈现$T^2$依赖性，这有效消除了衬底寄生电阻——这是发挥UWBG全部潜力的限制因素。由热容和晶格膨胀得到的德拜温度$\theta_{D,ScB_2}$约为850K，与$\theta_{D,ScB_2}$良好匹配，但低于Sc-rich生长条件下测得的1100K。我们讨论了德拜匹配作为衬底协同设计的关键标准，其在AlGaN生长过程中为散热和热匹配提供了显著的声子模式重叠。室温下53W/mK的竞争性热导率是全第一性原理计算值的一半，我们将这一差异归因于富硼生长产生的Sc空位。而电阻率约为理论值的2倍，表明电子和声子在热输运中扮演同等角色。约2.5nm rms粗糙度的光滑表面通过$\mathrm{ScB}_2$/AlGaN界面异质结构中的工程声子桥和声子极化激元实现先进散热模式，可能使功率处理能力比最先进的GaN/SiC提高约10-100倍。

英文摘要

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.

发表机构

• Morgan State University（摩根州立大学）
• Johns Hopkins University（约翰斯·霍普金斯大学）
• University of North Texas（北德克萨斯大学）
• National Lab for the Rockies（落基山国家实验室）
• Colorado School of Mines（科罗拉多矿业学院）
• U. of Colorado Boulder（科罗拉多大学博尔德分校）
• University of Virginia（弗吉尼亚大学）
• University of Maryland College Park（马里兰大学帕克分校）
• Towson University（陶森大学）

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