Variation in optical-absorption edge in SiN x layers with silicon clusters
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HOUS, VITREOUS, POROUS, ORGANIC, AND MICROCRYSTALLINE SEMICONDUCTORS; SEMICONDUCTOR COMPOSITES
Variation in Optical-Absorption Edge in SiNx Layers with Silicon Clusters M. D. Efremova^, V. A. Volodina, D. V. Marina, S. A. Arzhannikovaa, G. N. Kamaeva, S. A. Kochubeœa, and A. A. Popovb aInstitute
of Semiconductor Physics, Siberian Branch, Russian Academy of Sciences, ul. Institutskaya 4/1, Novosibirsk, 630090 Russia ^e-mail: [email protected] bInstitute of Microelectronics and Informatics, Russian Academy of Sciences, ul. Universitetskaya 21, Yaroslavl, 150007 Russia Submitted May 24, 2007; accepted for publication June 6, 2007
Abstract—Using optical methods, data on optical constants are obtained for silicon nitride films synthesized by plasma-chemical vapor deposition (PCVD). Models for calculating the permittivity in the model of inhomogeneous phase mixture of silicon and silicon nitride are considered. It is found that the optical-absorption edge (Eg) and the photoluminescence peak shift to longer wavelengths with increasing nitrogen atomic fraction x in SiNx films. When x approaches the value 4/3 characteristic for stoichiometric silicon nitride Si3N4, a nonlinear sharp increase in Eg is observed. Using Raman scattering, Si–Si bonds are revealed, which confirms the direct formation of silicon clusters during the film deposition. The relation between the composition of nonstoichiometric silicon nitride films, values of permittivity, and the optical-band width is established for light transmission. PACS numbers: 61.43.Dq, 64.70.Nd, 78.20.Ci, 81.05.Ge DOI: 10.1134/S1063782608020152
1. INTRODUCTION The interest in silicon nanocrystals caused by their possible use in designing memory elements [1] explains the stimulus for this investigation. Previously, it was shown that laser treatments are an acceptable tool for modifying silicon clusters in silicon nitride films obtained by pyrolitic decomposition [2]. The plasmachemical technique provides essentially lower temperatures of film deposition, which could be of importance for a number of applications, in particular, in technologies of fabrication of flat screens. In addition, the possibility of varying the energy gap of SiNx dielectric layers by an introduction of excess silicon atoms can optimize the potential barrier height for electrons and holes as well as the SiNx-film conductivity. In addition, an excess of silicon atoms during deposition can lead to the occurrence of silicon clusters, which can be chargestorage centers.
list the deposition parameters, including the ratio between gas fluxes under operation. The experimental technological installation includes the plasma-chemical reactor and the low-frequency oscillator (55 kHz). The electrode system in the reactor consists of four graphite parallel plates. The distance between the neighboring plates is 14 mm, and the plate size is 180 × 360 mm. The substrates are arranged on the electrode surface. The energy-supply system enables us to realize both continuous and pulsed modes of plasma generation. In the pu
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