Nitrogen Decoration of Basal-Plane Dislocations in 4H - SiC

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 ($\mathrm{N}$) doping promotes the conversion of BPDs to threading edge dislocations (TEDs) and improves the reliability of $4\mathrm{H}$-$\mathrm{SiC}$-based bipolar power devices. However, the interaction between $\mathrm{N}$ and BPDs, and the effect of $\mathrm{N}$ on the electronic properties of BPDs are still ambiguous, which significantly hinder the understanding on the electron-transport mechanism of $4\mathrm{H}$-$\mathrm{SiC}\text{\ensuremath{-}}$based bipolar power devices. Combining molten-alkali etching and the Kelvin probe force microscopy (KPFM) analysis, we demonstrate that BPDs create acceptorlike states in undoped $4\mathrm{H}$-$\mathrm{SiC}$, while acting as donors in $\mathrm{N}$-doped $4\mathrm{H}$-$\mathrm{SiC}$. 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 $4\mathrm{H}$-$\mathrm{SiC}$. The electron transfer from the defect states of intrinsic defects and native impurities to the unoccupied defect states of BPDs gives rise to the acceptorlike behavior of BPDs in undoped $4\mathrm{H}$-$\mathrm{SiC}$. Defect formation energies indicate that $\mathrm{N}$ atoms can spontaneously decorate BPDs during the $\mathrm{N}$ doping of $4\mathrm{H}$-$\mathrm{SiC}$. The binding between $\mathrm{N}$ and BPD is strong against decomposition. The accumulation of $\mathrm{N}$ dopants at the core of BPDs results in the accumulation of donorlike states at the core of BPDs in $\mathrm{N}$-doped $4\mathrm{H}$-$\mathrm{SiC}$. This work not only enriches the understanding on the electronic behavior of BPDs in $\mathrm{N}$-doped $4\mathrm{H}$-$\mathrm{SiC}$, but also helps understand the electron transport mechanism of $4\mathrm{H}$-$\mathrm{SiC}$-based bipolar power devices.