Embodiments include apparatuses, methods, and systems including a semiconductor photonic device having a waveguide disposed above a substrate. The waveguide has a first section including amorphous silicon with a first refractive index, and a second section including crystalline silicon with a second refractive index different from the first refractive index. The semiconductor photonic device further includes a heat element at a vicinity of the first section of the waveguide. The heat element is arranged to generate heat to transform the amorphous silicon of the first section of the waveguide to partially or completely crystallized crystalline silicon with a third refractive index. The amorphous silicon in the first section may be formed with silicon lattice defects caused by an element implanted into the first section. Other embodiments may also be described and claimed.