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Please use this identifier to cite or link to this item: http://hdl.handle.net/10087/8119

Title: Design, Analysis and Fabrication of Silicon-Based Optical Materials and Photonic Crystal Devices
Authors: Umenyi, Amarachukwu Valentine
ウメイニ, アマラチュク バレンタイン
Keywords: Silicon photonics
Photonic crystals
Si-ion implantation
Waveguides
Ultraviolet-light emission
Silicon nanocrystals
Finite-difference time-domain method
FDTD
Triangular lattice
Annealing
Issue Date: Sep-2010
Publisher: 群馬大学工学部
Abstract: As the integration of electronic components grow so does the need for low power, low cost, and high-speed devices. These have resulted in an increased need for complementary metal-oxide semiconductor (CMOS) compatible materials and fabrication technique for novel structures as well as accurate models of the electromagnetic eld behavior in them. Recent advances in materials technology and fabrication techniques have made it feasible to consider silicon (Si)-based optical materials and photonic crystal (PhC) de- vices having physical dimensions of the order of the optical wavelength as the possible means to achieve these needs. Research has shown that light emission from Si is possible in low-dimensional state, i.e., Si-nanocrystals (Si-ncs). Furthermore, three-dimensional (3-D) control of light compatible with CMOS fabrication technology is required in order to fully integrate optical functionalities into the existing Si-technology. However, the di - culties in the fabrication of 3-D PhC waveguides have resulted in using two-dimensional (2-D) PhC structures. Finally, numerical simulations pro- vide a framework for quick low-cost feasibility studies and allow for design optimization before devices are fabricated. In this dissertation, we present our e orts along these directions. This dissertation addressed the method of obtaining high quantum e ciency from Si-ncs compatible with CMOS processing. Si ions were implanted into a fused-silica substrate (10 mm 10 mm 1 mmt) at room temperature in the Takasaki ion accelerators for advanced radiation application (TIARA) of the Japan Atomic Energy Agency. The implantation energy was 80 keV, and the implantation amount was 2 1017 ions/cm2. The Si-implanted sub- strate was cut into four pieces (5 mm 5 mm 1 mmt) using a diamond-wire saw, and the four pieces were annealed in ambient air at 1100, 1150, 1200, and 1250 oC for 25 min in a siliconit furnace. PL spectra were measured at room temperature with excitation using a He-Cd laser ( =325 nm). Ultra- violet (UV)-PL spectra having peaks around a wavelength of 370 nm were observed from all the samples. In our experiments, the UV-PL peak had a maximum intensity after annealing at 1250 oC, and the longer wavelength PL peak around 800 nm observed from the samples annealed at 1100 and 1150 oC disappeared by annealing above 1200 oC. The two PL peaks of the Si-ion-implanted samples may have originated from interface layers be- tween Si-ncs and SiO2 media. However, we successfully obtained only the UV-light emission peaks by selecting the proper annealing temperatures. UV-light-emitting materials are expected to be useful as light sources for next-generation optical-disk systems whose data densities are higher than Blu-ray Disk systems. Additionally, this dissertation addressed the numerical modeling of PhC de- vices. Accurate computations can provide a detailed understanding of the complex physical phenomena inherent in PhC devices. The nite-di erence time-domain (FDTD) method, which is widely used by many researchers around the Globe, is a powerful tool for modeling PhC devices. We devel- oped a modi ed and easy FDTD method based on a regular Cartesian Yee's lattice for calculating the dispersion diagram of triangular lattice PhCs. Our method uses the standard central-di erence equation, which is very easy to implement in any computing environment. The Bloch periodic boundary conditions are applied on the sides of the unit cell by translating the periodic boundary conditions to match with the directions of periodicity in the tri- angular lattice. Complete and accurate bandgap information is obtained by using this FDTD approach. Convergence, accuracy, and stability analysis were carried out, which ensures the reliability of this method. Numeri- cal results for 2-D transverse electric (TE) and transverse magnetic (TM) modes in triangular lattice PhCs are in good agreement with results from 2-D plane wave expansion method. The obtained results are in consistence with the reported ones. To ease the practical application of this method, clear explanations on the computer implementation are also provided. Finally, this dissertation addressed the use of CMOS-compatible fabrication method and 2-D periodic structures to realize the control of light in 3-D. In particular, we designed, analyzed and fabricated novel PhC waveguides utilizing Si-ion implantation and 2-D periodic structures. The transport of ions in matter (TRIM) prediction of implantation depth distribution pro le (1 1017 ions/cm2, 80 keV) shows the range of about 150 nm. Assuming the e ective refractive index of the Si-rich region to be 1.89 and by using FDTD method, the PhC design parameters based on the telecommunication wave- length ( =1.55 m) were obtained by varying the radius to lattice constant ratio (r=a) from 0.2 to 0.45. We analyzed both TE and TM mode prop- agation in triangular-lattice PhCs. The designed parameters were found to be a=664 nm and r=a=0.35. The PBG spanned from normalized fre- quency of 0.39 to 0.46 [2 c/a] in the TE-mode triangular lattice and the gap to midgap ratio was 0.16. The designed pattern was fabricated and the diameter, the period and the depth of air holes of the waveguide were estimated by atomic force microscopy (AFM) to be 464, 666 and 175 nm, respectively. Numerical results using FDTD characterization show that, straight line PhC waveguides can achieve 100% transmission, while the 60o bend showed 80% transmission owing to the dispersion mismatch at the two 60o bends. These results may serve as useful guides and components in future high- density photonic integrated circuits associated with optical communications, computing, and signal processing.
Description: 学位記番号:工博甲404, 学位の種類:博士(工学)
URI: http://hdl.handle.net/10087/8119
Academic Degrees and number: 12301A000404
Degree name: 博士(工学)
Degree-granting institutions: 群馬大学
Appears in Collections:学位論文

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