Dangling bonds in a-Si:H revisited: A combined Multifrequency EPR and DFT Study

TL;DR

This study combines multifrequency EPR spectroscopy and DFT calculations to analyze dangling bonds in a-Si:H, revealing detailed g-tensor properties and defect delocalization, advancing understanding of paramagnetic defects in amorphous silicon.

Contribution

It provides high-resolution EPR data and compares experimental results with DFT models, highlighting defect delocalization in a-Si:H.

Findings

Rhombic g-tensor splitting with specific principal values

Pronounced g-strain indicating distribution of g-values

DFT models show less delocalization than experimental defects

Abstract

Multifrequency pulsed electron paramagnetic resonance (EPR) spectroscopy using S-, X-, Q- and W-Band frequencies (3.6, 9.7, 34, and 94 GHz, respectively) was employed to study paramagnetic coordination defects in undoped hydrogenated amorphous silicon (a-Si:H). The improved spectral resolution at high magnetic field reveals a rhombic splitting of the g-tensor with the following principal values: g_x=2.0079, g_y=2.0061 and g_z=2.0034 and shows pronounced g-strain, i.e., the principal values are widely distributed. The multifrequency approach furthermore yields precise ^{29}Si hyperfine data. Density functional theory (DFT) calculations on 26 computer-generated a-Si:H dangling-bond models yielded g-values close to the experimental data but deviating hyperfine interaction values. We show that paramagnetic coordination defects in a-Si:H are more delocalized than computer-generated dangling-bond defects and discuss models to explain this discrepancy.