The formation of stacking faults in heavily nitrogen-doped (mid-10(19) cm(-3)) 4H-SiC boules grown by the physical vapor transport (PVT) growth method was investigated by studying surface morphologies on the (000 (1) over bar) facet of the boules. Low-voltage scanning electron microscopy (LVSEM) observations detected stacking faults on the (000 (1) over bar) facet of heavily nitrogen-doped 4H-SiC crystals. LVSEM and atomic force microscopy (AFM) studies revealed that the stacking faults showed characteristic morphologies, which stemmed from the interaction between stacking faults and surface steps. These observations also revealed that heavy nitrogen doping resulted in the nucleation of a number of surface hillocks on the (000 (1) over bar) facet; the hillocks were never observed on the facet of conventionally doped (nitrogen concentration: mid-10(18) cm(-3)) 4H-SiC boules. Furthermore, the hillocks were nucleated only on the facet and never observed on the outer regions of the facet. Based on these results, the stacking fault formation mechanism in heavily nitrogen-doped 4H-SiC crystals is discussed. (C) 2017 Elsevier B.V. All rights reserved.