Gericke, Eicke; Melskens, J.; Wendt, R.; Wollgarten, M.; Hoell, A.; Lips, K.: Quantification of Nanoscale Density Fluctuations in Hydrogenated Amorphous Silicon. Physical Review Letters 125 (2020), p. 185501/1-6
10.1103/PhysRevLett.125.185501
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Abstract:
The nanostructure of hydrogenated amorphous silicon (a-Si∶H) is studied by a combination of smallangle x-ray scattering (SAXS) and small-angle neutron scattering (SANS) with a spatial resolution of 0.8 nm. The a-Si∶H materials were deposited using a range of widely varied conditions and are representative for this class of materials. We identify two different phases that are embedded in the a-Si∶H matrix and quantified both according to their scattering cross sections. First, 1.2 nm sized voids (multivacancies with more than 10 missing atoms) which form a superlattice with 1.6 nm void-to-void distance are detected. The voids are found in concentrations as high as 6 × 1019 cm−3 in a-Si∶H material that is deposited at a high rate. Second, dense ordered domains (DOD) that are depleted of hydrogen with 1 nm average diameter are found. The DOD tend to form 10–15 nm sized aggregates and are largely found in all a-Si∶H materials considered here. These quantitative findings make it possible to understand the complex correlation between structure and electronic properties of a-Si∶H and directly link them to the light-induced formation of defects. Finally, a structural model is derived, which verifies theoretical predictions about the nanostructure of a-Si∶H.