Quantification of Nanoscale Density Fluctuations in Hydrogenated Amorphous Silicon

The nanostructure of hydrogenated amorphous silicon a Si amp; 8758;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 amp; 8758;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 amp; 8758;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 amp; 8722;3 in a Si amp; 8758;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 amp; 8758;H materials considered here. These quantitative findings make it possible to understand the complex correlation between structure and electronic properties of a Si amp; 8758;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 amp; 8758;