| Summary: | 博士 === 國立成功大學 === 電機工程學系碩博士班 === 101 === Si-rich oxide (SRO) with embedded Si nanostructures has attracted considerable attention owing to pronounced quantum effect after annealing, regardless of the indirect band-gap nature of Si. The quantum-confinement properties of Si nanocrystals (NCs) have great potential for applications in light emission devices, photodetectors, and solar cells. Many methods have been reported to prepare the Si NCs embedded in SRO films, including sputtering, evaporation, and plasma-enhanced chemical vapor deposition. Among them, sputtering has several advantages superior to other methods such as low substrate temperature, low cost and good adhesion with substrates. Ion beam is another technique that has been developed to assist depositing optical thin films, particularly used together with evaporation to improve film quality. In this thesis, we prepared SRO films and SRO/SiO2 superlattices by sputtering and ion-beam-assisted sputtering (IBAS), and discus the material characteristic and optoelectric properties.
1. Self-assembled Si/SiO2 superlattice
This work involves as-prepared SiOx (x≦2) films that were deposited by reactive sputtering. The regular Si/SiO2 superlattices were self-assembled without post-annealing. The periodicity of Si/SiO2 superlattices was modulated by varying the oxygen flow rate, and was associated with x in SiOx in the range 2-1.3. Si/SiO2 superlattices were formed under compressive stress. The continuity equation of transport and the additional term in the Helmholtz free energy were used to explain the periodicity and the lower limit of the superlattices, respectively.
2. Si-rich oxide films
This study exploits the material and optical properties of Si NCs-embedded SRO films prepared by low-energy IBAS. Transmission electron microscopy and X-ray diffraction revealed that the IBAS improved crystallinity of the annealed SRO films. The size and density of Si NCs can be fine-tuned by ion-beam energy and oxygen partial pressure. The phase separation of IBAS-prepared SRO films was enhanced after annealing. This fact was particularly pronounced at low-oxygen partial pressure condition. Visible photoluminescence of the IBAS films was obtained, owing to the quantum confinement effect of Si NCs.
3. Si-rich oxide/SiO2 superlattices
This study presents the structure and luminescence properties of SRO/SiO2 superlattices in which the SRO layers were prepared by low-energy (〈60 eV) argon ion-beam-assisted sputtering. Experimental evidence indicates that the density of the Si NCs in the SRO layer was increased by ion-beam treatment after annealing, increasing the surface roughness. Moreover, the stoichiometry of the as-prepared SRO layer was unchanged but the phase separation of the annealed SRO layer was enhanced by the ion-beam treatment, yielding visible white photoluminescence from the E’ centers and Si nanocrystals.
4. Si-rich oxide/SiO2 superlattice LEDs
The SRO/SiO2 superlattices LEDs were prepared by varying the structure, substrate temperature, and ion source treatment was reported. The electroluminescences of SRO/SiO2 multilayers were associated with the injection barrier height and Si dots size. The retention time of SRO/SiO2 superlattice deposited by IBAS was longer than that prepared by sputtering. Impedance spectroscopy analyses were to realize the electrical properties of materials and their interfaces.
|
|---|
