Molecular Beam Epitaxially Deposited Amorphous Silicon

We have deposited a novel form of amorphous silicon through molecular beam epitaxy in an ultra-high vacuum. In particular, by depositing silicon atoms onto an optical quality fused quartz substrate at room temperature we have obtained a silicon-based material that lacks the periodicity that characterizes crystalline silicon but nevertheless has 98% of the density. Spectroscopic studies reveal that there are only trace amounts of hydrogen and other impurity atoms in this novel form of amorphous silicon, this contrasting dramatically with the case of conventional amorphous silicon. The Raman and optical spectroscopic properties of this form of amorphous silicon are contrasted with those of conventional amorphous silicon and sputtered amorphous silicon, and conclusions, regarding the amount of disorder, are drawn. Finally, the device implications of this novel form of amorphous silicon are discussed.