Combined multifrequency EPR and DFT study of dangling bonds in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>a</mml:mi></mml:math>-Si:H

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.