DIRECT FABRICATION OF SIGE CRYSTALLITES ON GLASS SUBSTRATE - FROM NANOCRYSTALS TO MICROCRYSTALS

We have found that a newly developed thermal CVD technique, reactive t hermal CVD, provided us with a powerful tool for fabricating SiGe crys tallites directly on a glass substrate from GeF4 and disilane. In an e arly stage of this film growth, crystalline nuclei occurred without an y accompanying amorphous deposit on the substrate at temperatures less than 450 degrees C. The grain size and population on the substrate we re easily tailored from nanocrystallites to microcrystallites and over several orders of magnitude in population by selecting growth conditi ons. Crystallinity was confirmed by Raman and transmission electron mi croscopy (TEM) combined with transmission electron diffraction (TED) s tudies. The experimental results suggested that there exist two differ ent mechanisms dominating the nucleation of crystallites on the substr ate, one of which is a heterogenous nucleation on the surface and the other a homogeneous nucleation in the gas phase near the surface.