The work deals with the highly important problem of the qualitative temperature dependence of avalanche breakdown voltage in p-n junctions based on 4H-SiC. As it has been shown before, the temperature coefficient of avalanche breakdown voltage (TCABV) is negative in seven SiC polytypes, including 4Н-SiC. This effect has been explained by the Wannier-Stark localization (WSL). It is worth noting that the plane of the investigated p-n junctions coincided with the basal plane (0001). However the current SiC device technology prefers 4H-SiC p-n junction formation on a plane that has 8о disorientation from (0001). This may result in a weakening of the WSL and, correspondingly, in a positive TCABV. This problem has been elucidated in the present paper. The photocurrent of 4H-SiC p-n junctions in a strong electric field has been scrutinized, that has allowed to discover a negative differential conductivity region and it has testified to the WSL process and negative TCABV.