Structure, Electronic And Optical Properties Of Er-doped Si-rich SiO₂ Thin Films And Reactivity Of Water With Pd-deposited MgO(100) Thin Films On Mo(100)

The achievement of efficient light emission from silicon is a crucial step towards realization of silicon-based optoelectronic integration. In these last ten years, erbium doping of silicon has been recognized as one of promising and attractive approaches. Moreover, the wavelength of 1.54 μm from its light emission is a standard wavelength in optical communication.This thesis mainly studies two approaches to fabricate erbium-doped silicon-rich silicon dioxide thin film on silicon using metal vapor vacuum arc (MEVVA) ion source implantation and erbium doped silicon multilayer by molecular beam epitaxy (MBE). In addition, the adsorption of water on Pd deposited epitaxial MgO(100) upon Mo (100) single crystals are also investigated as another part.Part I of this thesis discussed microstructure, electronic and optical properties of erbium-doped silicon-rich silicon dioxide thin films. In Chapter 3, the metal vapor vacuum arc ion source implantation is developed to synthesize the Er-doped Si-rich SiO₂ thin films under relatively low implanted ion energies and very high doses. Very high Er concentration of- 10²¹ atoms·cm^-3 in Si oxide layer could be reached, which are required for achieving efficient light emission from Er³⁺. The typical sample shows a 1.54 μm wavelength luminescence signal and its intensity decreases by only a factor of 2 with the measuring temperature increasing from 77 K to 300 K, showing very weak temperature quenching effect. Furthermore, the solubility, segregation and precipitation behaviors of high concentration are discussed as measured by XPS, RHEED, AFM, and XPS. The results show that silicon nanocrystals (nc-Si) have been formed in SiO₂ matrices during a rapid thermal annealing process at appropriate temperatures after dual-implantation. Reflective high energy electron diffraction and cross section transmission electron microscopic observations show that The sizes of nc-Si with good crystallinity are ranging from 2-6 nm in diameter and the average size of nc-Si is-4.5 nm.Since it is possible to think of applications where an amplifier is made by Er-doped SiO2 optical waveguides containing nc-Si with an Er excitation enhanced with respect to typical waveguides, it is necessary to acquire optimum parameters determined by the preparation conditions, in which it results in showing Er3+ efficient light emission with an ideal peak shape. Based on above consideration, the optical properties of the Er-doped Si-rich SiC>2 thin films are described in Chapter 4. In order to achieve optimum PL intensity, the thickness of SiC>2 film should be at least larger than the projective range of Si and Er implantation. More than 90 run SiO2 film was thick enough to the distribution of implanted Si and Er atoms within SiC>2 film. The Er ion dose for highest PL intensity at 77 K and RT are lxlO16 cm'2 and 5xl016 cm"2, corresponding to Er concentrations of 4.5x1020 and 4xlO21 cm'3. The optimized Si ion dose is3⁵xl017 cm"2 when the Er concentration is relatively high (1020 1021 Er cm"3).The complexity of the annealing temperature dependence of the 1.54 um luminescence intensity may be related to nucleation and growth of nc-Si, defects and damages, and the activation of Er +. The highest PL intensity in our case can be achieved after RTA at 1000 °C -1100 V for 20 s.Chapter 5 discusses the correlation between the light emission around 1.54 um related to Er and the light emission in visible region of Er-doped Si-rich SiC>2, in which nc-Si are embedded. The experimental evidences might support the model of strong coupling between excitons and Er ions in SiC>2 thin films containing nc-Si prepared by a MEVVA ion source. Corresponding mechanisms of the light emission around 1.54 um related to Er have been discussed when the Er concentration in Si-rich SiC>2 films could reach the order of 1021 cm"3.In Chapter 6, we present a new approach to fabricate Er-doped Si multilayer, which consists of alternative Er-O-codoped Si layers and O-doped layers, grown by MBE. Er3+-related luminescence from the sample has much higher intensity, narrower peak width and weak temperature quenching than that of Er-O-codoped Si monolayer. The possible explanation is that Si excitons confined in c-Si of O-doped Si layer can transfer to neighboring Er3+ ions in Er-O-codoped layer by a tunneling process, resulting in an enhancement of PL at 1.54 jam.