XPS Studies of Hydrogen and Oxygen Bonding Configurations in Hydrogenated Microcrystalline Silicon Materials Produced by

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XPS STUDIES OF HYDROGEN AND OXYGEN BONDING CONFIGURATIONS IN HYDROGENATED MICROCRYSTALLINE SILICON MATERIALS PRODUCED BY NEUTRON IRRADIATION Y.C. Koo*, G.C. Weatherly**, R.Sodhi§, S.J.Thorpet and K.T. Austt *IBM Canada, Dept. 458, 844 Don Mills Rd. North York, Ont. M3C 1V7 Canada **McMaster University, Material Science and Engineering, Hamilton, Ont. Canada §Center for Biomaterial, U of Toronto, 170 College St. Toronto, Ont. Canada tMetallurgy and Material Science, U of Toronto, 184 College St. Toronto, Ont. Canada ABSTRACT The bonding of Si atoms in gc-Si:H thin films has been investigated using X-ray photoelectron spectroscopy (XPS) in conjunction with infra-red spectroscopy (IR), secondary ion mass spectroscopy (SIMS) and analytical electron microscopy (TEM/EDX/EELS) data. By using aSi:H and single crystal silicon as reference samples, structural and hydrogen effects could be assessed, since both a-Si:H and gc-Si:H have a similar concentration of hydrogen based on the N 15 hydrogen profiling data, but different structures. On the other hand, single crystal silicon and gtc-Si:H both have a diamond cubic structure based on electron diffraction data, but single crystal silicon contains little or no hydrogen except adsorbed at the surface. Based on the XPS and IR data, charge transfer of the Si2 core level towards a deep lying level was observed in the gic-Si:H material. IR measurements showed a large amount of hydrogen was located in the grain boundaries. The charge transfer is mainly due to a change in the hydrogen bonding configuration. A well bonded oxide is formed in the ttc-Si:H material near the surface with an almost complete absence of the Si3 + intermediate oxide state. The presence of a large amount of hydrogen (25 at.%) even at a high volume fraction (70%) of pIc-phase may limit the oxidation and promote better oxide formation. The variation of the quality of the oxide/ltc interface could be a possible explanation for the different photoluminescence observed by various groups for porous gtc-Si material. INTRODUCTION The physical, electrical and optical properties of materials depend upon their structure. Pure amorphous silicon, a-Si, contains a large defect concentration in the material as a result of poor strain accommodation. The presence of hydrogen in the amorphous film compensates for most of the defect gap states by passivating dangling bonds. The hydrogen may also decorate grain boundary in polycrystalline or g±c-material to improve the electrical or optical properties. The renewed interests of the role of hydrogen in silicon is enhanced by the recent reports of light emitting porous silicon and work related to poly silane alloys [1-3]. In this study various techniques were used in conjunction with XPS to understand hydrogen and surface oxygen bonding configuration effects during the phase transformation from amorphous to g.tc-Si:H material. EXPERIMENTAL Microcrystalline Si:H thin films were produced by neutron irradiation-induced crystallization of amorphous Si:H with approximately 25 at.% hydrog