Despite the decades of development of the single-crystal growth and homoepitaxy of 4H silicon carbide (4H-SiC), high-density threading dislocations (TDs) still remain in 4H-SiC. In this work, we show that the diameters, depths, and inclination angles of molten-alkali etched pits can be employed to discriminate threading edge dislocations (TEDs), threading screw dislocations (TSDs), and threading mixed dislocations (TMDs) in 4H-SiC. The formation of etch pits of TEDs, TSDs, and TMDs during molten-alkali etching is found to be assisted by the dislocation line, dislocation step, and successively dislocation line and step, respectively. By inspecting the surface potentials of n-type 4H-SiC with Kelvin probe force microscopy (KPFM), we show that both TSDs and TEDs behave as donors in n-type 4H-SiC, which gives rise to charge depletion at TDs in n-type 4H-SiC. TDs are found to participate in the broad band D1 luminescence of 4H-SiC, as evidenced by the fact that the microphotoluminescence (micro-PL) intensities at the centers of TDs are stronger than those in dislocation-free regions of 4H-SiC. Understandings gained in this work may help the optimization of n-type 4H-SiC by manipulating the electronic and optical properties of TDs.

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Discrimination of dislocations is critical to the statistics of dislocation densities in 4H silicon carbide (4H-SiC), which are routinely used to evaluate the quality of 4H-SiC single crystals and homoepitaxial layers. In this work, we show that the inclination angles of the etch pits of molten-alkali etched 4H-SiC can be adopted to discriminate threading screw dislocations (TSDs), threading edge dislocations (TEDs) and basal plane dislocations (BPDs) in 4H-SiC. In n-type 4H-SiC, the inclination angles of the etch pits of TSDs, TEDs and BPDs in molten-alkali etched 4H-SiC are in the ranges of 27°−35°, 8°−15° and 2°−4°, respectively. In semi-insulating 4H-SiC, the inclination angles of the etch pits of TSDs and TEDs are in the ranges of 31°−34° and 21°−24°, respectively. The inclination angles of dislocation-related etch pits are independent of the etching duration, which facilitates the discrimination and statistic of dislocations in 4H-SiC. More significantly, the inclination angle of a threading mixed dislocations (TMDs) is found to consist of characteristic angles of both TEDs and TSDs. This enables to distinguish TMDs from TSDs in 4H-SiC.

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In this letter, we optimize the flatness of 4H silicon carbide (4H SiC) wafers by tuning the sequence-of single-sided lapping, enlightened by the different mechanical properties of the Si face and C face of 4H-SiC. After wire sawing, the coarse lapping and fine lapping are carried out to rapidly remove the surface damages and optimize the flatness of 4H-SiC wafers. From the point of view of controlling the values of the bow and warp of 4H-SiC wafers, the coarse-lapping sequence of the C-face lapping followed by Si-face lapping is beneficial, while the preferred fine-lapping sequence is Si-face lapping followed by C-face lapping. Nanoindentation tests indicate that the C face has higher hardness and lower fracture toughness the Si face. This gives rise to thicker surface damages at the C face after the wire sawing. After removing the same amount of wire-sawing induced surface damages, the thickness of residual surface damages of the C face is higher than that of the Si face after the coarse lapping. Since the fine lapping basically removes all the surface damages, and creates near-perfect C face and Si face. The higher amount of surface damages of the C face after the coarse lapping and the higher fracture toughness of the near-perfect Si face after the fine lapping can tolerate more plastic deformations, which gives rise to the superior flatness of the C-face followed-by-Si-- face coarse lapped and the Si-face-followed-by-C-face fine lapped 4H-SiC wafers, respectively.