The temperature rise in GaN-on-SiC based high electron mobility transistors (HEMTs) is firmly dependent on the thermal conductivity (k) of GaN epilayer and the interfacial thermal conductance (G) between GaN and SiC. The AlN buffer is usually utilized during the heteroepitaxial growth of GaN on SiC substrate, while the effects of its thickness on k and G are still not clear. In this study, the GaN/AlN/SiC multilayer structure is prepared by metal–organic chemical vapor deposition, and aiding by time-domain thermoreflectance, we detect how the thickness of AlN interlayer influences k and G. The results reveal that the AlN interlayer evolves from serrated island shape to smooth planar form with increasing its thickness from 13 to 104 nm, which induces that the tensile stress of the subsequently grown GaN firstly decreases and then increases, giving a minimum value of 339 MPa at 52 nm-thick AlN. Consequently, a maximal k of 150 W m⁻¹ K⁻¹ for the GaN epilayer is achieved. Moreover, the AlN interlayer is beneficial to the enhancement of G due to the improved overlap of phonon density of states, and an increase of G by up to 64% can be realized via an insertion of 104 nm-thick AlN, which could be the consequence of both atomically smooth interfaces and the improved crystal quality of thicker AlN. The findings clearly manifest the effect of AlN interlayer thickness on the k and G of GaN/AlN/SiC structures, which provides guidelines for preparation of multilayer structures helping to minimize the thermal resistance of HEMTs.

中文翻译：

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GaN-on-SiC 异质结构中 AlN 层间厚度对 GaN 外延层和 GaN/SiC 界面热导率的影响


基于 GaN-on-SiC 的高电子迁移率晶体管 （HEMT） 的温升在很大程度上取决于 GaN 外延层的热导率 （k） 以及 GaN 和 SiC 之间的界面热导率 （G）。AlN 缓冲液通常在 GaN 在 SiC 衬底上的异质外延生长过程中使用，而其厚度对 k 和 G 的影响尚不清楚。在本研究中，通过金属-有机化学气相沉积制备了 GaN/AlN/SiC 多层结构，并借助时域热反射法检测了 AlN 中间层的厚度如何影响 k 和 G。结果表明，随着 AlN 厚度从 13 nm 增加到 104 nm，AlN 夹层从锯齿状岛状演变为光滑的平面状，这导致随后生长的 GaN 的拉伸应力先减小后增大，在 52 nm 厚的 AlN 下最小值为 339 MPa。因此，GaN 外延层的最大 k 为 150 W m ⁻¹ K ⁻¹ 。此外，由于声子态密度重叠的改善，AlN 夹层有利于 G 的增强，并且通过插入 104 nm 厚的 AlN 可以实现高达 64% 的 G 增加，这可能是原子平滑界面和较厚 AlN 的晶体质量改善的结果。研究结果清楚地表明了 AlN 层厚度对 GaN/AlN/SiC 结构的 k 和 G 的影响，这为多层结构的制备提供了指导，有助于最大限度地减少 HEMT 的热阻。