FORMATION OF NANOCRYSTALLINE STRUCTURES IN AMORPHOUS THIN-FILMS OF GERMANIUM

The formation of nanocrystalline structures during the amorphous-to-crystalline transition for thin films of Ge prepared by physical vapour deposition has been studied by high resolution electron microscopy. Crystallization at below one half of the melting temperature of Ge was achieved during deposition or afterwards by an annealing treatment. The structural evolution of the nanocrystalline fabric of the Ge films, originating from the amorphous phase, proceeds by heterogeneous nucleation and twin dominated growth. The main structural features formed during the crystallization include: (i) multiply twinned crystallites nucleated at pre-formed embryos; (ii) growth twinning introduced by errors in the stacking of atoms during crystallization; and (iii) deformation twinning due to elastic strains induced in the films during growth.