Etch pit investigation of free electron concentration controlled 4H-SiC

Etch pits were investigated using the molten KOH selective etching method to examine dependence of etch pit shape and size on free electron concentration. The free electron concentrations of highly doped 4H-silicon carbide (SiC) were controlled by proton irradiation and thermal annealing, which was confirmed by a frequency shift in the LO-phonon–plasmon-coupled (LOPC) mode on micro-Raman spectroscopy. The proton irradiated sample with 5×1015 cm−2 fluence and an intrinsic semi-insulating sample showed clearly classified etch pits but different ratios of threading screw dislocation (TSD) and threading edge dislocation (TED) sizes. Easily classified TEDs and TSDs on proton irradiated 4H-SiC were restored as highly doped 4H-SiC after thermal annealing due to the recovered carrier concentrations. The etched surface of proton irradiated 4H-SiC and boron implanted SiC showed different surface conditions after activation.

► Free electron concentrations of 4H-SiCs were controlled by proton irradiation and thermal annealing.
► Etch pits of dislocations with different electron concentrations were investigated.
► Penetration depths of protons were estimated by quasi-longitudinal optical frequency shift.
► Free electron concentrations of 4H-SiCs were estimated by longitudinal optical phonon–plasmon coupled mode.