Erbium Doped Silicon as an Optoelectronic Semiconductor Material

In this thesis, the materials aspects of erbium-doped silicon (Si:Er) are studied to maximize Si:Er luminescence intensity and to improve Si:Er performance as an optoelectronic semiconductor material. Studies of erbium (Er) and silicon (Si) reactivity, erbium diffusion and solubility in silicon, Si:Er heat treatment processing with oxygen and fluorine co-implantation and the mechanism of Si:Er light emission have been carried out to define optimum processing conditions and to understand the nature of optically active centers in Si:Er. In the erbium and silicon reactivity studies, a ternary phase diagram of Er-Si-O was determined. ErSi 2_x(X = .3) was found to be the most stable erbium silicide formed on single crystal silicon, and it could be oxidized in the presence of oxygen (02). These findings confirm the results that erbium precipitates as ErSi2_(x = .3) in silicon and erbium clusters with oxygen to form complexes in Si:Er with oxygen co-implantation. Luminescence studies on various erbium compounds established a unique spectrum for Si:Er, which can be used to fingerprint products of Si:Er processing. The diffusivity and solubility of Er in Si are determined based on the analysis of changes in implanted Er SIMS profiles of Si:Er after high temperature annealing (1150 13000C). Er is a slow diffuser with moderate solubility in Si. The diffusivity of Er in Si D(Er) is 5 x 1011cm 2 /s at 1200°C with a migration energy of 4.6eV, at a rate similar to Ge in Si. The equilibrium solid solubility of Er in Si [Er], is , 101 l 6atoms/cm 3 between 1150 13000C, similar to S in Si. The low Er diffusivity in Si enables metastable concentrations of Er to be incorporated into Si at levels far exceeding the equilibrium solid solubility of 10 16 atoms/cm 3. Furthermore, the low diffusivity and high oxidation tendency make Si:Er process compatible with existing Si fablines, since cross contamination during heat treatment is minimized. Post-implantation annealing and ligand enhancement are essential to achieve luminescence in Si:Er. The heat treatment process of Si:Er and the impact of oxygen (O) and fluorine (F) ligands have been studied. The Si:Er heat treatment process is determined by three internal processes in Si:Er: (1) implantation damage anneal; (2) ligand impurity outdiffusion; and (3) formation and dissociation of optically active Er-ligand complexes. Fluorine is found to be 100 times more effective than oxygen in enhancing luminescence intensity in Si:Er under the similar processing conditions. In Si:Er co-doped with F, Er-F associates, most likely ErF3 , are the optically active center, responsible for the light emission. A process model has been constructed to simulate the physical processes occurring in Si:Er during the heat treatment. The simulation includes the processes of the complexes formation and dissociation, and the ligand outdiffusion and exhibits their limiting role in determining the luminescence intensity. The optimum heat treatment condition to achieve maximum light emission in Si:Er is constrained by the process of implantation damage anneal. Light emission studies at different measurement temperatures show the presence of the thermal quenching of Si:Er luminescence: a sharp decrease of luminescence intensity at measurement temperatures above 200K. An energy back transfer process of non-radiative de-excitation of Er3 + excited states to Si lattice is proposed as the most likely mechanism in Si:Er. Si:Er is demonstrated as a potential optoelectronic semiconductor material, compatible with current Si technology. The Si:Er light emission intensity can be increased by maximizing metastable Er-ligand complexes in Si:Er through optimizing processing conditions. The optimal process of high performance Si:Er photonic devices can be achieved by controlling the metastable kinetics of Si:Er. Thesis Supervisor: Lionel C. Kimerling Title: Professor