Absence of an abrupt phase change from polycrystalline to amorphous in silicon with deposition temperature

Using fluctuation electron microscopy, we have observed an increase in the mesoscopic spatial fluctuations in the diffracted intensity from vapor-depo sited silicon thin films as a function of substrate temperature from the am orphous to polycrystalline regimes. We interpret this increase as an increa se in paracrystalline medium-range order in the sample. A paracrystal consi sts: of topologically crystalline grains in a disordered matrix; in this mo del the increase in ordering is caused by an increase in the grain size or density. Our observations are counter to the previous belief that the amorp hous to polycrystalline transition is a discontinuous disorder-order phase transition.