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

Authors

Parthapratim Biswas, University of Southern MississippiFollow
Durga Paudel, University of Southern MississippiFollow
Raymond Atta-Fynn, University of Texas at Arlington
David Drabold, Ohio University
Stephen R. Elliott, University of Cambridge

Document Type

Article

Publication Date

2-13-2017

Department

Physics and Astronomy

School

Mathematics and Natural Sciences

Abstract

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.

Publication Title

Physical Review Applied

Volume

7

First Page

1

Last Page

10

Recommended Citation

Biswas, P., Paudel, D., Atta-Fynn, R., Drabold, D., Elliott, S. R. (2017). Morphology and Number Density of Voids In Hydrogenated Amorphous Silicon: An Ab Initio Study. Physical Review Applied, 7, 1-10.
Available at: https://aquila.usm.edu/fac_pubs/17233