VLPCVD Heteroepitaxial Growth of Very Thin GE-Layers on Si-Substrates

Abstract

ABSTRACTBy Pulsed Gas CVD-growth, heteroepitaxial growth of pure Ge-layers from pure GeH4 has been accomplished at 650 °C on Si-substrates without intermediate Si1−xGex-bufferlayers. The material has been studied by means of RBS, SEM, ECP, XRD and cross-sectional, highresolution and plan-view TEM. The thickness of the Ge-layers varied between 2 and 24 monolayers. From 5 monolayers on, some part of the Ge appears to be fully relaxed. Uptill 12 monolayers, the growth is fully 2-dimensional and results in specular, flat surfaces; for thicker layers islanding starts (Stranski-Krastanow growth). The material is completely defect-free. According to XRD-measurements, the perpendicular strained Ge-cell dimension is 5.748 Å, which is very reproducible for all layer-thicknesses. Nevertheless, from linear elastic theory considerations, it should be 5.83 Å. The Ge-layers so formed appear to be suitable for use in short-period (SinGem)p-superlattices.