Spectroscopic Ellipsometry Studies of Tb-doped SiO2 Thin Films
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Spectroscopic Ellipsometry Studies of Tb-doped SiO2 Thin Films Chu Wan Huang1, Zhe Chuan Feng1, Yia Chung Chang2, and Ting Kai Li3 1 Graduate Institute of Electro-Optical Engineering & Department of Electrical Engineering, National Taiwan University, Taipei, 106-17, Taiwan 2 Academia Sinica, Research Center for Applied Sciences, 128 Section 2, Academia Road Nankang, Taipei, 115, Taiwan 3 Sharp Labs of America, Inc., 5700 Pacific Rim Blvd, Camas, WA, 98607 ABSTRACT The optical properties of Tb-doped SiO2 films have been studied from multi-wavelength spectroscopic ellipsometry (SE) measurements performed over the 250–1100 nm wavelength range. The SE modeling carried out with care to adhere as much to the ellipsometric fitting qualities. The refractive index dispersions, the layer thickness, and the lateral thickness variation of the films are given and discussed regarding the optical constitution of these films and the ellipsometric validity of these parameters. The measurements revealed important structural changes as a function of annealing temperature which provide an interesting inside into the annealing kinetics of ion-implanted Tb-doped SiO2 films, and also demonstrate the importance of spectroscopic ellipsometry in determining nondestructively the dielectric functions in materials that have undergone complex processing. An optical model was developed using SE data obtain optical properties—refractive index n and extinction coefficient k for Tb-doped SiO2. Generalized anisotropy and depolarization are measurable using rotating compensator ellipsometers or controlled retarders for partial Muller Matrix analysis. Rotating compensator ellipsometers allow accurate and rapid in situ diagnostics, including window birefringence calibration. Steady progress has been made in both ex situ and in situ ellipsometry hardware, software, and application. INTRODUCTION Silicon based optoelectronics integration offers promising opportunity for low-cost solutions to optical communications and interconnects. Achieving optical implification and lasing in silicon has been one of the most challenging goals in silicon photonics because bulk silicon is an indirect band gap semiconductor and therefore has very low light emission efficiency. Light emission in silicon has thus focused on the use of silicon engineered materials such as nanocrystals, Si/SiO2 superlattices, rare earth-doped silicon-rich oxides, surface-textured bulk silicon and Si/SiGe quantum cascade structures, in which Tb doped SiO2 films are very interesting materials for the optoelectronics device applications [1, 2]. Ellipsometry is an optical measurement of the polarization change occurring when light interacts (reflection and transmission) with materials [3, 4]. Model-based regression is limited to the information content available from the experimental data. For this reason, ellipsometry is often performed at multiple angles and wavelengths to increase the available information [5]. Reflection from a bulk, isotropic substrate with no coatings or over lay
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