Molten-alkali etching has been widely used to reveal dislocations in 4H silicon carbide (4H-SiC), which has promoted the identification and statistics of dislocation density in 4H-SiC single crystals. However, the etching mechanism of 4H-SiC is limited misunderstood. In this letter, we reveal the anisotropic etching mechanism of the Si face and C face of 4H-SiC by combining molten-KOH etching, X-ray photoelectron spectroscopy (XPS) and first-principles investigations. The activation energies for the molten-KOH etching of the C face and Si face of 4H-SiC are calculated to be 25.09 and 35.75 kcal/mol, respectively. The molten-KOH etching rate of the C face is higher than the Si face. Combining XPS analysis and first-principles calculations, we find that the molten-KOH etching of 4H-SiC is proceeded by the cycling of the oxidation of 4H-SiC by the dissolved oxygen and the removal of oxides by molten KOH. The faster etching rate of the C face is caused by the fact that the oxides on the C face are unstable, and easier to be removed with molten alkali, rather than the C face being easier to be oxidized.

中文翻译：

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4H-SiC 的各向异性蚀刻机制：实验和第一性原理见解

熔碱刻蚀已广泛用于揭示4H碳化硅（4H-SiC）中的位错，促进了4H-SiC单晶位错密度的识别和统计。然而，4H-SiC 的刻蚀机理被误解的程度有限。在这封信中，我们通过结合熔融KOH刻蚀、X射线光电子能谱（XPS）和第一性原理研究，揭示了4H-SiC的Si面和C面的各向异性刻蚀机理。4H-SiC的C面和Si面的熔融KOH蚀刻的活化能分别为25.09和35.75 kcal/mol。C面的熔融KOH蚀刻速率高于Si面。结合XPS分析和第一性原理计算，我们发现4H-SiC的熔融KOH蚀刻是通过溶解氧对4H-SiC的氧化和熔融KOH去除氧化物的循环进行的。C面的蚀刻速率较快是因为C面的氧化物不稳定，更容易被熔碱去除，而不是因为C面更容易被氧化。