Electronic and Optical Properties of Threading Dislocations in n-Type 4H-SiC

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.