| The heteroepitaxy of gallium arsenide on silicon provides a means of combining gallium arsenide optoelectronic devices and high-speed electronics with silicon integrated circuits. While gallium arsenide/silicon technology has advanced considerably in the past few years, problems with the structural quality of the gallium arsenide/silicon films greatly impede further progress. The aim of the work described in this dissertation is an understanding of the initial stages of gallium arsenide/silicon growth and their effects on the quality of the gallium arsenide layers. All of the films were grown by molecular beam epitaxy (MBE) and analyzed by a number of characterization methods, including transmission electron microscopy (TEM), Rutherford backscattering spectrometry (RBS), and reflection high energy electron diffraction (RHEED).; Gallium arsenide/silicon nucleation occurs in the form of islands, which are compressively strained in the plane of the film due to the 4% lattice mismatch. As the islands gradually coalesce to form a complete film, the film crystallinity improves considerably, and the strain relaxes as a result of misfit dislocation formation. We find that island formation causes surface morphology degradation, and island coalescence appears to be the source of additional defects. Beginning the growth with a low-temperature buffer layer greatly improves the surface morphology without degrading the crystallinity of thick films. Both ion channeling and cross-sectional TEM show a marked change in the defect density in the region of the buffer layer/overlayer interface.; The silicon substrates we employed had been intentionally misoriented from (100) in order to create a staircase of steps on the silicon surface. Cross-sectional TEM images show that these steps tend to form step bands during the substrate heat treatment prior to the growth. The vast majority of the gallium arsenide islands nucleate at these step bands and grow along them. The island shape depends on the degree and direction of the substrate misorientation from the (100) surface normal, reflecting the underlying step arrangement. The planar compressive strain within the islands is affected by these steps as well. The implications of these findings on the optimal substrate misorientation and preparation procedure are discussed. |
