Shedding light on the growth of amorphous, polymorphous, protocrystalline and microcrystalline silicon thin films

We focus here on a study of the growth of polymorphous and protocrystalline silicon materials with respect to the well-established amorphous and microcrystalline silicon. Protocrystalline films correspond to a slow crystallization process, in which the films grow densely in the first monolayers, but their porosity and roughness increase with thickness, allowing the nucleation of crystallites, and finally the formation of a microcrystalline phase. On the contrary, polymorphous films remain dense, independent of their thickness. The control of the temperature gradient between the RF electrode and the substrate holder allows a switch from microcrystalline to polymorphous silicon growth, which strongly supports our hypothesis of polymorphous films being formed by simultaneous contributions of silicon radicals and clusters to the growth.