Mechanisms of Visible Photoluminescence from Size-Controlled Silicon Nanoparticles
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Mechanisms of Visible Photoluminescence from Size-Controlled Silicon Nanoparticles Toshiharu Makino*, Nobuyasu Suzuki, Yuka Yamada, Takehito Yoshida, Ikurou Umezu1, and Akira Sugimura1 Advanced Technology Research Laboratories, Matsushita Electric Industrial Co., Ltd., 3-10-1 Higashimita, Tama-ku, Kawasaki 214-8501, Japan 1 Department of Physics, Faculty of Science and Engineering, Konan University, 8-9-1 Okamoto, Higashinada-ku, Kobe 658-8501, Japan * Present address: High Technology Research Center, Konan University, 8-9-1 Okamoto, Higashinada-ku, Kobe 658-8501, Japan
ABSTRACT We have observed visible photoluminescence (PL) spectra (peak energy: 3.1 eV) of size-controlled silicon (Si) nanoparticles annealed in oxygen gas. The PL peak energy did not depend on the temperature, and the PL lifetime was relatively fast (on the order of nanoseconds). It was inferred that the visible PL was attributed to localized states in the oxidized surfaces of size-controlled Si nanoparticles. We also observed the PL excitation spectra and studied the excitation process. In order to elucidate mechanisms of the visible PL, excitation and recombination processes are discussed.
INTRODUCTION It is well known that group IV elements (Si, Ge) are capable of emitting strong visible light at room temperature when the size reduces to the nanometer region [1]. Recently, various methods to form nanostructured Si have been studied. However, it has been difficult to develop nanoparticles into advanced functional devices because they have a large surface to volume ratio, and are extremely sensitive to impurities and/or damage. Light-emitting properties of the nanoparticles, particularly light-emitting wavelength and efficiency, strongly depend on their mean sizes, size distributions [2], and surface conditions [3]. Pulsed laser ablation (PLA) in inert background gas (PLA-IBG) is one of the promising methods to form nanoparticles [4,5], because cold-walled clean processing which excites only beam-focused areas. Size-controlling of nanoparticles can be precisely performed by low-pressure-operated differential mobility analyzers (LP-DMA) which can be combined into the PLA-IBG formation units [6,7]. Surface conditions of nanoparticles can be controlled by annealing in ambient gas after deposition of nanoparticles on a substrate [3,8]. In this paper, we report the light-emitting properties of visible PL of size-controlled Si nanoparticles (np-Si). After controlling surface conditions of the np-Si by annealing in oxygen (O2) gas, broad visible PL spectra were observed at room temperature. In order to elucidate mechanisms of the visible PL, excitation and recombination processes are discussed from observations of time-resolved and steady-state spectra, and PL excitation spectra.
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EXPERIMENTS
RESULTS AND DISCUSSION After controlling surface conditions of np-Si by annealing in O2 gas, broad visible PL spectra (peak energy: 3.1 eV) were observed. Figure 1 shows the influence of the annealing conditions on PL spectra of the np-Si excited
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