Properties of amorphous silicon/amorphous silicon-germanium multilayers

Abstract

A comprehensive study of multilayer structures made of hydrogenated and fluorinated amorphous silicon and its alloy with germanium, a-Si:H,F/a-Si,Ge:H,F, is reported. After briefly describing the deposition process and the chemical composition of the samples, the optical and the electronic properties of the multilayers are concentrated on. Raman scattering spectra suggest mixing over a 1-nm-thick interfacial layer. Auger electron spectra combined with sputter profiling and x-ray linewidth are compatible with this observation. The rise in optical band gap observed as the a-Si,Ge:H,F well layer thickness is reduced below 5 nm is also compatible with this interfacial mixing. No extra defect states above the detection limit of 2×1010 cm−2 are associated with the interfaces. Electron transport parallel to the layers takes place in the well layers. Perpendicular electron and hole transport is dominated by elastic tunneling through thin (<5 nm) barrier layers, and by thermal emission over thicker barriers.