Rare Earth-Doped Si-Based Thin Films

Since the discovery of the efficient sensitization of rare earth ions (RE) by nanometer sized Si clusters (Si-ncls), intense efforts have been focused on the study of the coupling Si-ncls:RE because of the promising solutions to gather electrical and optical efficient components on the same wafer compatible with the CMOS technologies. Thus Si-ncls:Er³⁺ systems have concentrated the most important works during this last decade. Silica is the commonly used host matrix in which Si excess has been incorporated to provide Si-ncls upon a suitable annealing treatment. However, such a system does not show till now a relevant net optical gain allowing the possible transfer of the technology to the industry. This can partially be attributed to numerous losses processes (cross relaxation processes, confined career absorption, reabsorption process etc…, ) occurring in such optical devices. An interesting point concerns the fact that the sensitizing of RE ions can be achieved not only via Si-ncls, but also via other radiative channels that can open the development of new devices. Indeed, recently, Nd- and Tb- as well as Tb-Yb-doped layers have attracted attention because of their potential applications in laser, light source and solar cell, respectively.

The aim of this talk is to give an overview of our recent results achieved on rare earth doped Si-rich matrices produced by reactive magnetron sputtering for Si-based light emitting materials or solar cell layers. Different host matrices such as SiO_x, Si_xO_yN_z, SiN_x, Hf_xSi_yO_wN_z, … have been investigated with the aim to enhance the quantum efficiency of the emission of the rare earth ion. Depending on the intended application, optimisations of the emission properties have been carried out by means of deposition parameters, specific annealing treatments (classical or rapid thermal annealing), structures (single- or multilayers). The achieved results have been interpreted using on the one hand the framework of Maxwell equations (solved by a Finite Difference Time Domain (FDTD) method) coupled to Auxiliary Differential Equations (ADE) describing guided modes propagation as well as the concentration of rare earth and Si-ncls in different states resulting in estimation of gain and on the other hand a light extraction model in layered media. Specific spectroscopic experiments have been performed to determine the excitation mechanism according to the host matrix used. Finally, typical devices produced and studied will be described.

This work is supported by French National Agency (ANR) through GENESE-ANR Blanc and INTERREG MEET (Materiel for Energy Efficiency in transport) projects.