Growth and High Resolution Tem Characterization of Ge x Si 1-x /Si Hetero-Structures by Remote Plasma-Enhanced Chemical
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GROWTH AND HIGH RESOLUTION TEM CHARACTERIZATION OF GexSil-x/Si HETERO-STRUCTURES BY REMOTE PLASMA-ENHANCED CHEMICAL VAPOR DEPOSITION R. Qian, I. Chung, D. Kinosky, T. Hsu, J. Irby, A. Mahajan, S. Thomas, S. Banerjee, A. Tasch, Microelectronics Research Center; L. Rabenberg, Center for Materials Science and Engineering, The University of Texas at Austin, Austin, TX 78712; C. Grove, Motorola Inc., Austin, TX 78721; and C. Magee, Evans East, Inc., Plainsboro, NJ 08536
ABSTRACT Remote Plasma-enhanced Chemical Vapor Deposition (RPCVD) has been used to grow GexSil.x/Si heteroepitaxial thin films at low temperatures (-450*C). In situ RHEED has been used to confirm that smooth, single crystal heteroepitaxial films can be grown by RPCVD. Plan-view and cross-sectional TEM have been employed to study the microstructure of the heteroepitaxial films. Lattice imaging high resolution TEM (HRTEM) has shown perfect epitaxial lattice alignment at the heterojunction interfaces. GexSil.x/Si films which exceed their CLT's appreciably show dense Moir6 fringes under plan-view TEM. The spacings between the fringes have been used to estimate the relaxed lattice constants. In addition to the inhomogeneous strain observed in XTEM, Selected Area electron Diffraction (SAD) analysis of the interfaces displays two split patterns. The spacings between the diffraction spots have been used to calculate the lattice constants in the epitaxial films in different crystal directions, which agree very well with the prediction by Vegard's law as well as the estimate from planview TEM analysis. HRTEM analysis also reveals the crystallographic nature of the interfacial misfit dislocations in the relaxed films.
INTRODUCTION Growth of GexSilix/Si epitaxial heterostructures has received considerable attention for their potential applications in novel column IV material-based electronic and optical devices. Among other attractive properties, GexSil-x/Si heterostructures provide promising opportunities in energy bandgap engineering [1], in which it is possible to adjust the energy bandgap by controlling the Ge concentration in an epitaxial film, and to change the energy band alignment by choosing appropriate states of strain in the underlying layers. These features can be used to overcome performance limits in traditional silicon-based technology. GexSil-x/Si heterostructures also have considerable potential in integrated optoelectronics. Although it is well known that Si and Ge are both indirect band gap materials, optical absorption can be enhanced by the zone-folding-induced quasi-direct bandgap nature of superlattice structures [2]. It has been shown that electrical and optical properties of GexSil.-xSi devices are sensitive to their crystalline microstructure. For example, bandgap lowering shows much stronger dependence on the Ge concentration in strained GexSil-x layers than in unstrained layers. These material characteristics are directly related to the lattice mismatch between Si and Ge, which plays a profound role in determining the microstructure of
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