Multi-Band Electron Paramagnetic Resonance Study of Microcrystalline and Cluster Silicon Embedded in SiO 2
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Multi-Band Electron Paramagnetic Resonance Study of Microcrystalline and Cluster Silicon Embedded in SiO2 Takashi Ehara, Tadaaki Ikoma1 and Shozo Tero-Kubota1 School of Science and Engineering, Ishinomaki Senshu University Shinmoto 1, Minamisakai, Ishinomaki, Miyagi 986-8580, Japan 1 Institute for Chemical Reaction Science, Tohoku University Katahira 2-1-1, Aoba-ku, Sendai, Miyagi 980-8577, Japan ABSTRACT Dangling bond defects (DB) in silicon microcrystallines and clusters embedded in SiO2 have been studied by X- and Q-band electron paramagnetic resonance (EPR) spectroscopy. The EPR spectra due to the DB were remarkably depending on the grain size, which was controlled by annealing temperature. The microcrystalline containing film shows a broad and unsymmetrical EPR signal at g = 2.006 with the line width of 13 G in X-band spectra. The signal can be simulated by using the anisotropic g-values of Pb center. The Si cluster samples obtained from the annealing at less than 800°C give an asymmetric EPR spectra at about g = 2.004 with the line width of about 9 G in X-band. The EPR signal due to the E’ center was also observed. INTRODUCTION Cluster and microcrystalline Si embedded in SiO2 matrixes have been investigated actively [1-3]. Co-sputtering of the Si and SiO2, followed by thermal annealing produces the grains of the Si in the SiO2. Using this method, photoluminescence (PL) from the Si clusters have been reported [3]. The study using the Si embedded in SiO2 structure is useful in other kinds of studies, because the properties of Si grain can be studied without the effects of amorphous fraction. In the case of hydrogenated microcrystalline silicon (µc-Si:H), the crystalline grains are embedded in amorphous silicon (a-Si:H) [4]. Thus, the results observed in any method, such as optical absorption or electrical properties, have been affected by the existence of the a-Si:H. In the case of electron paramagnetic resonance (EPR) study, the signal of silicon dangling bond defects (DB) is observed with that in the amorphous fraction [5,6]. Thus, it is very difficult to clarify the properties of the DB in the crystalline fraction independently. In the present work, the EPR spectra of the microcrystalline and the cluster Si embedded in the SiO2 are studied using X-band and Q-band EPR spectroscopy. The properties of the DB are discussed with the structural properties of the Si grains. EXPERIMENTAL DETAILS The samples were prepared by the rf co-sputtering method and the thermal annealing. Twenty-four pieces of crystalline Si wafers cut into 0.5 mm x 5 mm x 15 mm section were placed on a SiO2 target (10 cm in diameter, purity of 99.99%) and co-sputtered with Ar gas at sputtering pressure of 2.66 Pa. The film depositions were carried out at a rf power of 200 W (13.56 MHz) for 3 hours using an HSR551 sputtering machine (Shimadzu). Thin films at a thickness of about 1.5 µm were deposited. The thermal annealing for 1 hour was carried out at 600°C, 800°C and 1000°C in a nitrogen atmosphere.
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