Evolution of the microstructure in microcrystalline silicon prepared by very high frequency glow-discharge using hydrogen dilution

A series of samples was deposited by very high frequency glow discharge in a plasma of silane diluted in hydrogen in concentrations SiH4/(SiH4 + H-2) varying from 100% to 1.25%. For silane concentrations below 8.4%, a phase t ransition between amorphous and microcrystalline silicon occurs. Microcryst alline silicon has been characterized by transmission electron microscopy ( TEM) and x-ray diffraction. The medium-resolution TEM observations show tha t below the transition, the microstructure of microcrystalline silicon vari es in a complex way, showing a large variety of different growth structures . For the sample close to the phase transition, one observes elongated nano crystals of silicon embedded in an amorphous matrix followed at intermediat e dilution by dendritic growth, and, finally, at very high dilution level, one observes columnar growth. X-ray diffraction data evidence a (220) cryst allographic texture; the comparison of the grain sizes as evaluated from TE M observations and those determined using Scherrer's equation illustrates t he known limitations of the latter method for grain size determination in c omplex microstructures. (C) 2000 American Institute of Physics. [S0021-8979 (00)07005-5].