Thermal Transformation of Hydrogen Bonds in a-SiC:H Films: Structural and Optical Properties
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Thermal Transformation of Hydrogen Bonds in a-SiC:H Films: Structural and Optical Properties Andrey V. Vasin, Sergey P. Kolesnik, Andrey A. Konchits, Vladimir S. Lysenko, Alexey N. Nazarov, Andrey V. Rusavsky, S. Ashok1 Lashkaryov Institute of Semiconductor Physics, Kiev. Ukraine 1 The Pennsylvania State University, University Park, USA ABSTRACT Hydrogenated amorphous silicon carbide (a-SiC:H) films have been deposited using magnetron sputtering technique. Investigation of the effect of the vacuum annealing temperature on photoluminescence properties and paramagnetic defects, and its correlation with structural transformation of a-SiC:H have been performed. Significantly enhanced light emission efficiency after low-temperature vacuum treatment (450 oC) is found due to enhanced passivation of paramagnetic defects associated with carbon-rich chemically disordered structure. Subsequent high-temperature vacuum annealing results in a decrease of luminescent intensity that is associated with increase of carbon related paramagnetic defect states, shown to be the primary nonradiative recombination centres. For the first time silicon-related dangling bonds in a-SiC:H have been detected reliably by electron paramagnetic resonance measurements in annealed samples.
INTRODUCTION The hydrogenated amorphous silicon-carbon alloy film (a-SiC:H) has attracted interest as a wide band-gap material having light emitting properties in the visible spectral range. In such a heteronuclear noncrystalline material, besides structural disorder (distortion of the length and angle of the bonds) there is a chemical disorder of local coordination (the presence of homonuclear Si-Si and C-C bonds). Moreover the dangling bonds should be related both to silicon and carbon atoms. The situation can be also complicated by a variety of possible electron configurations of the carbon atoms. In fact one may expect several types of carbon-related unpaired electrons i.e. spins associated with σ-orbitals for both sp2 and sp3 hybridization and πorbitals for sp2 hybridization. To our knowledge there has not been any systematic study of the different contributions of silicon and carbon- related defects to the luminescent properties of aSi1-xCx:H. In the present study, we have attempted to link the visible light emission to the structure and defect configurations of near-stoichiometric a-SiC:H films that had been subjected to vacuum anneals.
EXPERIMENTAL DETAILS Amorphous hydrogenated silicon carbide films were deposited by reactive magnetron sputtering of a monocrystalline silicon target using a mixture of Ar (60 vol. %) + CH4 (40 vol. %) as working gas. Quartz as well as (100) n-type Si wafers, polished on both sides, were used
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as substrates. After deposition, the silicon and quartz substrates were cut into pieces and annealed in vacuum (10-6 Torr) for 15 minutes over the temperature range 200 – 850 oC. The samples were analyzed by Auger-electron spectroscopy (AES), photoluminescence (PL), electron paramagnetic resonance (EPR), UV-VIS transm
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