  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.
