Quantum confinement in mixed phase silicon thin films grown by co-deposition plasma processing

• Carriers in crystalline Si nanodots remain quantum confined in the presence of an hydrogenated amorphous Si matrix.
• The energies covered by a single PL band show both that there is quantum confinement and that the origin is due to defects.
• The temperature dependence of the PL band suggests that these nanocrystals possess fewer defects than those grown by conventional PECV.
• Co-deposition of Si nanodots in an hydrogenated amorphous Si matrix is a novel method for making active layers for solar cells.

Mixed phase, hydrogenated amorphous and nanocrystalline silicon thin films grown by co-deposition (nanocrystals and amorphous material deposited sequentially in the same vacuum system) demonstrate pronounced quantum confinement effects. Based on photoluminescence measurements of co-deposited samples, we find evidence that the optical gap of nanocrystals embedded in hydrogenated amorphous silicon is increased to energies exceeding bulk crystalline silicon values – at least as high as 1.35 eV. The broad spectrum of emission of the nanocrystals is attributed to the size distribution and local fluctuations in matrix hydrogenation. The temperature dependence of this PL suggests that these nanocrystals possess fewer defects than those grown by conventional plasma enhanced chemical vapor deposition methods. Interactions between electronic states in nanocrystals and localized states in amorphous silicon matrix tissues are discussed in terms of their role in determining the strength of the quantum confinement potential.