Properties of amorphous semiconducting $\frac{a-\mathrm{S}\mathrm{i}:\mathrm{H}}{a-\mathrm{Si}{\mathrm{N}}_x:\mathrm{H}}$ multilayer films and of $a-\mathrm{Si}{\mathrm{N}}_x:\mathrm{H}$ alloys

We prepared, by plasma deposition and by alternating the plasma-gas mixture, multilayer films consisting of sequential layers of hydrogenated amorphous silicon ($a$-Si: H) of thickness $d_1$ and insulating amorphous silicon nitride ($a-\mathrm{Si}{\mathrm{N}}_x:\mathrm{H}$) of thickness $d_2$. The thickness $d_2$ was held constant at 24 Å, while $d_1$ was changed from 12 to 2120 Å. Films with small $d_1$ had up to 180 layers pairs. The conduction and optical properties of these multilayer films were studied as well as the effect of prolonged light exposure (Staebler-Wronski effect). At large sublayer thickness $d_1>100\mathrm{}$ Å the properties are dominated by space-charge doping which raises the Fermi level in the $a$-Si: H layers and leaves the nitride layers positively charged. At small sublayer thicknesses $d_1<50\mathrm{}$ Å our observations are consistent with those of Abeles and Tiedje and their interpretation in terms of quantum-well confinement of charge carriers in the thin semiconductor sheets sandwiched between large-band-gap insulating layers. The properties of these multilayer films are compared with those of $a-\mathrm{Si}{\mathrm{N}}_x:\mathrm{H}$ alloys. These were prepared under the same plasma-decomposition conditions by changing the plasma-gas composition ratio of ${\mathrm{NH}}_3$ to Si${\mathrm{H}}_4$ from 0.02 to 10.