Characteristics and behaviors analysis of etch pits in 4H-SiC epilayers by molten KOH etching

The etch rates of molten-alkali etching fluctuates among different types of 4H-SiC epilayers, due to Fermi levels variations. This inconsistency makes it challenging to identify dislocations based solely on etch pit shapes and sizes. The three-dimensional characteristics of etch pits in 4H-SiC epilayers by molten alkali (KOH) etching were characterized. Through analysis of the dislocation strain fields, the inclination angles of etch pits have been adopted to distinguish basal plane dislocations (BPDs), threading edge dislocations (TEDs) and threading screw dislocations (TSDs) in epilayer. The angles for BPDs, TEDs and TSDs are in the range of 2 $°$-5 $°$, 7 $°$-12 $°$ and 29 $°$-44 $°$, respectively, regardless of doping types or etch time. Measurements of etch pit angle variations demonstrated that dislocations extending along the c-axis produce larger etch pits compared to those whose extension deviates from the c-axis. The mechanism underlying changes in etch pit shape was analyzed via depth profiles. The conversion of BPDs to TEDs at the substrate-epilayer interface induces a hexagonal-to-elliptical morphological transition of etch pits with prolonged etching time. This study provides fundamental insights into the dislocation etching mechanisms in 4H-SiC epilayers and develops a reliable analytical method for precise dislocation characterization.