TEM Investigation of Polar-on-Nonpolar Epitaxy: GaAs-AlGaAs on (100) Ge

摘要

Morphologically excellent GaAs and AlGaAs epitaxial layers have been grown on (100) Ge substrates by molecular-beam epitaxy (MBE). Transmission electron-microscopy (TEM) studies of the thin-film cross sections revealed that defects, most probably antiphase domains, were contained within a 20 to 30 nm thick initial layer near the GaAs/Ge interface, formed with a 0.1- mu m/h growth rate at 500 degrees C. A reduction of defects occurred in the remaining 0.1- mu m thick layer, for which the growth rate and temperature had been increased to 1 mu m/h and 580 degrees C, respectively. The interface between this GaAs layer and a subsequently grown 35-nm thick AlAs film was found to undulate with a period of 150 to 200 nm and an amplitude of 5 to 10 nm. Such large undulations were not observed in AlGaAs-GaAs superlattices grown after an additional deposition of 2- mu m GaAs. High-resolutin electron-microscopy observations suggest that transitions between different layers are abrupt on the atomic scale. In addition, modulation-doped field-effect transistors fabricated on these layers had similar characteristics to those obtained with MBE layers grown on GaAs substrates. These results demonstrate that the (100) Ge surface is suitable for MBE polar-on-nonpolar semiconductor growth and that the integration of III-V films with silicon electronic devices via epitaxial Ge on Si is feasible, provided that epitaxial Ge of sufficient quality grown on Si is available. (ERA citation 10:018891)