Morphology and Number Density of Voids In Hydrogenated Amorphous Silicon: An Ab Initio Study

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Physics and Astronomy


Mathematics and Natural Sciences


We present a first-principles study of the formation and structure of microvids in device-quality models of hydrogentated amorphous silicon (a−Si : H). Using a combination of classical metadynamics and first-principles density-functional calculations, which is capable of generating large a−Si : H models with a linear size of several nanometers and a realistic hydrogen distribution, we examine the morphology and compute the number density of microvoids at low and high concentrations of hydrogen. The results of our calculations are compared with experimental data from small-angle x-ray scattering and hydrogen and implanted-helium effuson measurements. Our study suggests that the number density of microvoids is the order of (7−8) × 1018 cm-3 for device-quality models with (8−10)‐at. % H, and which increases to (1−3) × 1019 cm-3 with an increase of hydrogen content to 18 at. %. We find the morphology of the microvoids to be highly complex with a radius of gyration varing from 2.7 to 5.0 Å for very large models. The spatial distributions of microvoids at low and high concentrations are strongly influneced by the presence of isolated and interconnected voids, respectively, which are consistent with the results from hydrogen and implanted-helium effusion measurements. The simulation methodology and results presented here have direct applications in large-scale modeling of a−Si : H/c−Si heterojunctions with intrinsic thin-layer technology for the development of next-generation silicon solar cells and resistive switching mechanisms in ultra-low-power nonvolative memory devices, such as chalcogenide- or oxide-based conductive bridging random-access-memory devices.

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Physical Review Applied



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