Spectroscopic Study of Rare Earth Doped Nano-Crystalline Silicon in Sio 2 Films
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SPECTROSCOPIC STUDY OF RARE EARTH DOPED NANO-CRYSTALLINE SILICON IN SiO2 FILMS C. ROZO, L. F. FONSECA, O. RESTO, S. Z. WEISZ Physics Department, University of Puerto Rico at Rio Piedras, San Juan, PR, USA
ABSTRACT Si-rich SiO2, Nd-doped Si-rich SiO2 and Nd-doped SiO2 thin films were prepared. Photoluminescence (PL) spectra for visible and infrared were obtained for each as-deposited film. The samples were annealed by steps to different temperatures within the range 600°C1100°C for 30 minutes at each annealing temperature. PL spectra were obtained at each step and their characteristics were studied. The best annealing temperature for the PL of the rare earth (RE) ions was obtained. The PL spectra of the films were compared with one another. Energy transfer from the silicon nanocrystals (Si nc) to the RE ions is verified using excitation wavelength and excitation power spectra.
INTRODUCTION Since the first report of a Nd2O3–doped glass used as a laser material [1] different types of glass hosts have been produced in order to improve and understand laser action of RE doped glasses and glass properties. Spectroscopic research of rare earth doped glasses has been done on bulk glasses, fiber glasses, and thin films of glass type hosts. This has led to the development of bulk glass lasers, fiber lasers, waveguides, optical amplifiers, and diodes [2,3]. To improve the PL of RE ions in glass hosts it is very important that the hosts have large bandgaps, low phonon energies, high transparency in the wavelength ranges of the excitation and PL of the RE ions, very low concentration of impurities that can absorb energy from the RE ions enhancing the non-radiative relaxation and quenching the PL of the RE ions [2,3,4]. Due to the small absorption cross-sections of RE ions [4, 5], sensitizers are used to enhance the absorption and improve the PL of these ions. Si nanoparticles (nanocrystals) have been used as sensitizers for Er3+ ions to enhance their emission at 1.54µm [6]. High concentration co-doping of Er along with nc-Si in SiO2 has been performed with no reported concentration quenching, as opposed to the much lower solubility of Er in SiO2 [7]. The effective absorption cross-sections estimated for the Er3+ 1.54 µm emission are ~ 4 orders of magnitude higher than in other known hosts, and the pumping for such emission can be performed using a larger variety of pumping bands [7,8]. Research has also included the study of Yb3+-doped Si nc [9], Eu-doped Si nc [10], as well as Nd3+-doped Si nc and Tm3+-doped Si nc [11]. This paper presents an initial study of the annealing behavior of the infrared and visible PL spectra of Nd-doped SiOx samples prepared by rf co-sputttering. A motivation for the study besides the application to laser diodes, optical amplifiers, and waveguides for wavelength division demultiplexing (WDM), is the application towards short range optical inter-satellite linking (SROIL) [12].
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EXPERIMENTAL Nd2O3-doped and non-doped Si-rich SiO2, as well as Nd2O3-doped SiO2 samples were prepared b
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