Informative Aspects of Molten KOH Etch Pits Formed at Basal Plane Dislocations on the Surface of 4H‐SiC

Abstract

Despite being a destructive technique, molten KOH etch pits at basal plane dislocations are found to have informative aspects, as revealed by photoluminescence imaging and optical microscopy, on the 4° off‐cut (0001) surface of 4H‐SiC p–i–n diode chips, where single Shockley‐type stacking faults have expanded during electroluminescence experiments. Smaller etch pits are observed aligning on single lines along ±[100] that are the shallowest sides of stacking faults. Through closer observation of the pits, the facing directions are found to agree well with a model explaining the two types of partial dislocations constituting the line. Other basal plane dislocation pits are observed by scanning electron microscopy on the sublimation‐grown wafer surface before epitaxial growth. The distances between the partial dislocation cores are measured at each pit. No basal plane dislocation etch pit facing toward ±[100] is found, but a weak correlation is noted between the partial dislocation distance at the cores and the direction that the basal plane dislocations face. The corresponding results are discussed in terms of the image force and the force exerted on steps perpendicular to the (0001) plane, to understand the mechanisms of basal plane dislocation propagation and/or conversion to threading edge dislocations.

Single Shockley stacking fault expansion from immobile basal plane dislocations in 4H-SiC

“…The governing driving force that bent the BPD can be attributed to the image force acting on the step surface. 16,47) On the right side of the substrate/epilayer interface in Fig. 2, the lower PD line was gradually bent toward the [1120] direction.…”

Partial dislocation structures at expansion terminating areas of bar-shaped single Shockley-type stacking faults and basal plane dislocations at the origin in 4H-SiC

“…3(b), indicating that the remaining PD lines are along the Peierls valley, namely, the ±[ 2110] and ±[ 12 10] directions. The zigzag structure of the KOH etch pits was observed on the terminating line of the triangular 1SSF that corresponds to 30°Si(g) and 90°Si(g) PDs, 33) where the direction of the etch pits formed on the 90°S i(g) PDs was not symmetric with the 30°Si(g) PDs. However, the zigzag shape observed in Fig.…”

Dislocations in 4H silicon carbide

“…The average size of the etch pits of TSDs is about two times larger than that of TEDs [107,108]. The preferential etching of BPDs in off-axis sliced 4H-SiC starts at the outcrop at the surface, and proceeds along the dislocation line of a BPD, which creates the sea-shell shaped etch pit [109,110]. In order to increase the shape difference among etch pits of different dislocations, additives, such as NaOH, K 2 CO 3 , Na 2 O 2 and MgO, have been added into molten KOH to facilitate the identification and statistics of different dislocations in 4H-SiC [111][112][113].…”