Increased medium-range order in amorphous silicon with increased substrate temperature

Using fluctuation electron microscopy, we have measured the medium-range order of magnetron sputtered silicon thin films as a function of substrate temperature from the amorphous to polycrystalline regimes. We find a smooth increase in the medium-range order of the samples, which we interpret in the context of the paracrystalline structural model as an increase in the size of and/or volume fraction occupied by the paracrystalline grains. These data are counter to the long-standing belief that there is a sharp transition between amorphous and polycrystalline structures as a function of substrate temperature.