The dependence of the interface and shape on the constrained growth of nc-Si in a-SiNx/a-Si:H/a-SiNxstructures

Size-controlled nanocrystalline silicon (nc-Si) has been prepared from a-SiN x /a-Si:H/a-SiN x ('a' standing for amorphous) structures by thermal annealing. Transmission electron microscope analyses show that the lateral size of the nc-Si is controlled by the annealing conditions and the a-Si sublayer thickness. The deviation of the nc-Si grain size distribution decreases with the a-Si sublayer thickness, so thinner a-Si sublayers are favourable for obtaining uniform nc-Si grains. In the a-Si:H (10 nm) sample annealed at 1000ºC for 30 min, an obvious bi-modal size distribution of nc-Si grains appears, but no obvious bi-modal size distribution is found in other samples with thinner a-Si:H sublayers. On the basis of the experimental results, we discuss the process of transition from the sphere-like shape to the disc-like shape in the growth model of the nc-Si crystallization. The critical thickness of the a-Si sublayer for the constrained crystallization can be determined by the present model. Moreover, the increase of the crystallization temperature in the ultrathin a-Si sublayer is also discussed.