TEM characterization of SiGeC material system

Abstract

The IV-IV material system, specifically Si1-xGex/Si, has generated considerable interest in the scientific community in recent years. The built-in compressive strain and composition of pseudomorphic Si1-xGex epilayers on Si substrates affect the band structure and energy gap, which are fundamental to bandgap engineering. This property has been used in demonstrating a heterojunction bipolar transistor with SiGe base, resulting in improved high-frequency performance over conventional transistors with Si bases. However, the thermal instability and lower critical thickness of Si1-xGex layers limits applications, in turn prompting investigation of the Si1-x-yGexCy system. Substitutional carbon incorporation in Si1-xGex is expected to relieve the strain in the epilayer and increase the energy gap, the latter being an important consideration in revolutionizing transistor technology. Recently, growth and characterization of pseudomorphic Si1-x-yGexCy and its photoluminescence properties have been reported.In our present study, we have characterized Si1-x-yGexCy samples grown on Si substrates by chemical vapor deposition. Different precursors and flow rates were used tovary the relative elemental compositions. Rutherford backscattering and secondary ion mass spectroscopy techniques were employed for compositional analysis and transmission electron microscopy was used to determine microstructure. Electron transparent specimens were prepared in cross-section by a standard technique, involving mechanical grinding, dimpling and argon ion-milling. TEM observations were made with JEOL 2000FX and JEOL 4000EX microscopes. Selected area diffraction patterns and optical diffractograms were used in determining the structure and lattice constants.