Detailed structural analysis of GaAs grown on patterned Si

The growth of GaAs on patterned Si substrates is essential for the integration of GaAs and Si devices. Moreover this growth may have to be done in wells to planarize the surfaces of the Si and GaAs devices for their interconnection. In this study, GaAs is grown by MBE on such patterned Si substrates, with window width down to 3 μm, and a complete structural characterization of the material is made by electron microscopy. In every case, SEM observations show a very good definition of the pattern by the contrast of the flat surface of the monocrystalline GaAs compared to the very rough surface of the polycrystalline GaAs. Cross-sectional observations by STEM or TEM on non-etched samples reveal that the quality of the monocrystalline GaAs is at least as good in terms of defect density as that of the standard GaAs on Si. On samples etched with a plasma to produce wells, grains often form against the Si sidewall. Chemical etching with lateral etching avoids contact of the growing GaAs with the Si sidewall and subsequent grain formation. The crystalline quality obtained on etched samples is not as good as on non etched samples. A way of preparing the wells to improve this crystalline quality is proposed.