High-pressure chemical vapor deposition (HPCVD) can be used to deposit high quality, atomically smooth hydrogenated amorphous silicon (a-Si:H) within micrometer to nanometer sized silica fibers. In this process, a high-pressure mixture of silane and helium (at ~30 MPa) flows within a microcapillary, and the microcapillary wall is heated to facilitate the silane decomposition reaction resulting in semiconductor film deposition. Void-free filling of the microcapillary template is desirable in order to improve optical quality by lowering transmission losses.  However, complete filling of the fiber over a length of centimeters is challenging in view of the fiber’s extreme aspect ratio. We present a kinetic model for high-pressure silane decomposition by using reactive molecular dynamics simulations of silane pyrolysis reactions (using REAXFF) to identify the key reaction steps in the decomposition process. The developed decomposition kinetics are then incorporated into a computational model for silicon film growth within the fiber. The model predictions correlate well with experimentally-measured film thickness profiles.

Optimizing high-pressure chemical vapor deposition processes for void-free filling of silica optical fiber microcapillaries with hydrogenated amorphous silicon

251st National Meeting (2016)

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