4 H- SiC中基面位错的氮装饰
Nitrogen decoration of basal plane dislocations in 4H-SiC
摘要：
基面位错（BPD）对4 H-SiC双极功率器件的可靠性提出了很大的挑战。大量的氮掺杂促进了BPD向穿透刃位错（TEDs）的转化，提高了4 H-SiC基双极功率器件的可靠性。然而，N与BPDs之间的相互作用以及N对BPDs电子性质的影响仍不明确，这严重阻碍了对4 H-SiC基双极功率器件电子输运机理的理解。结合熔融碱蚀刻和开尔文探针力显微镜（KPFM）分析，我们证明，BPD创建受体类状态在未掺杂的4 H-SiC，而作为施主在N掺杂的4 H-SiC。第一性原理计算证实了BPD在未掺杂的4 H-SiC的价带最大值（VBM）以上产生占据的缺陷态，在导带最小值（CBM）以下产生未占据的缺陷态.在未掺杂的4 H-SiC中，电子从本征缺陷和原生杂质的缺陷态转移到BPD的未占据缺陷态，导致BPD的类受主行为。缺陷形成能表明，在4 H-SiC的N掺杂过程中，N原子可以自发地修饰BPD。N和BPD之间的结合是强的，以防止分解。N掺杂的4 H-SiC中，N掺杂在BPD核的积累导致了类施主态在BPD核的积累。这一工作不仅丰富了对N掺杂4 H-SiC双极器件中BPD电子行为的理解，而且有助于理解4 H-SiC基双极功率器件的电子输运机理。
英文摘要：
Basal-plane dislocations (BPDs) pose a great challenge to the reliability of bipolar power devices based on the 4H silicon carbide (4H-SiC). It is well established that heavy nitrogen (N) doping promotes the conversion of BPDs to threading edge dislocations (TEDs) and improves the reliability of 4H-SiC-based bipolar power devices. However, the interaction between N and BPDs, and the effect of N on the electronic properties of BPDs are still ambiguous, which significantly hinder the understanding on the electron-transport mechanism of 4H-SiC-based bipolar power devices. Combining molten-alkali etching and the Kelvin probe force microscopy (KPFM) analysis, we demonstrate that BPDs create acceptor-like states in undoped 4H-SiC, while acting as donors in N-doped 4H-SiC. First-principles calculations verify that BPDs create occupied defect states above the valence band maximum (VBM) and unoccupied defect states under the conduction-band minimum (CBM) of undoped 4H-SiC. The electron transfer from the defect states of intrinsic defects and native impurities to the unoccupied defect states of BPDs gives rise to the acceptor-like behavior of BPDs in undoped 4H-SiC. Defect formation energies indicate that N atoms can spontaneously decorate BPDs during the N doping of 4H-SiC. The binding between N and BPD is strong against decomposition. The accumulation of N dopants at the core of BPDs results in the accumulation of donor-like states at the core of BPDs in N-doped 4H-SiC. This work not only enriches the understanding on the electronic behavior of BPDs in N-doped 4H-SiC, but also helps understand the electron transport mechanism of 4H-SiC-based bipolar power devices.
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