FORMATION OF NANOCRYSTALLINE STRUCTURES IN AMORPHOUS THIN-FILMS OF GERMANIUM

The formation of nanocrystalline structures during the amorphous-to-cr ystalline transition for thin films of Ge prepared by physical vapour deposition has been studied by high resolution electron microscopy. Cr ystallization at below one half of the melting temperature of Ge was a chieved during deposition or afterwards by an annealing treatment. The structural evolution of the nanocrystalline fabric of the Ge films, o riginating from the amorphous phase, proceeds by heterogeneous nucleat ion and twin dominated growth. The main structural features formed dur ing the crystallization include: (i) multiply twinned crystallites nuc leated at pre-formed embryos; (ii) growth twinning introduced by error s in the stacking of atoms during crystallization; and (iii) deformati on twinning due to elastic strains induced in the films during growth.