Comparison of the Strain and Stress in Bonded and Epitaxial Gallium Arsenide on Silicon by Photoreflectance Spectroscopy
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M8.5.1
Comparison of the Strain and Stress in Bonded and Epitaxial Gallium Arsenide on Silicon by Photoreflectance Spectroscopy Measurements Spyros Gallis1, George Deligeorgis and Alexandros Georgakilas Microelectronics Research Group, FORTH, IESL and Physics Department, University of Crete, P.O. Box 1527, 711 10 Heraklion, Greece; Marin Alexe Max Planck Institute of Microstructure Physics, Weinberg 2, D-06120 Halle, Germany. ABSTRACT The presence of an internal strain arising from the GaAs/spin-on-glass (SOG)/Si bonding procedure was investigated. In addition, the magnitude of any residual stress at room temperature and the mechanisms that may impose a stress, leading to elastic or plastic deformation of the bonded GaAs films, were identified. A comparative study of biaxial strain and stress, as a function of temperature in the range of 80- 300 K, in a bonded 2 µm-thick GaAs/SOG/Si sample and in an epitaxial 2 µm-thick GaAs/Si sample, grown by molecular beam epitaxy (MBE), will be presented. The type and magnitude of strain were determined by photoreflectance spectroscopy. In the case of GaAs/SOG/Si, the strain in the GaAs layer was found to be negligible, with compressive character, at room temperature and tensile in all other measured temperatures, whereas for the epitaxial GaAs/Si, the strain was taking significant tensile values in all temperatures. Furthermore, the strain for both samples was increasing with temperature reduction, as it is expected for a thermal strain induced by the different thermal expansion coefficients of GaAs and Si. The comparative study indicated clearly that the bonded GaAs/SOG/Si films are essentially strain-free at room temperature. This is a very important result for the good reliability of laser diodes that can be processed from such bonded GaAs material, which also has a crystal quality similar to that of the available GaAs substrates. INTRODUCTION The wafer scale integration of III-V optoelectronic devices with Si CMOS circuits can result into semiconductor components with improved performance and/or new functionalities [1]. Two alternative GaAs-Si material integration processes have been investigated for this purpose; the heteroepitaxial growth of GaAs-on-Si (GaAs/Si) and the low temperature bonding of GaAs and Si wafers using a spin-on-glass (SOG) intermediate layer (GaAs/SOG/Si). The presence of crystalline defects and internal strains in the III-V semiconductor films is critical for the reliability of fabricated laser diodes and thus it becomes very important to study these issues in the two alternative GaAs-on-Si structures.
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Current address: CESTM, University at Albany, 251 Fuller Road, Albany, NY 12203, USA
M8.5.2
To estimate the internal strain in a 2 µm GaAs/SOG/Si sample (#133) as well as a reference 2 µm epitaxial GaAs/Si sample (#66), the energy band-gap shift from the gap of an unstrained GaAs substrate was determined, by the photoreflectance (PR) technique. EXPERIMENTAL AND FITTING DETAILS The experimental set-up for the PR measurement was essentially the sa
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