Semiconductor substrate cleaning and surface morphology in molecular beam epitaxy

In-situ laser light scattering shows that the surface morphology of GaAs substrates during the initial stages of homoepitaxial growth is a sensitive indicator of substrate cleanliness. Oxide removal by atomic-hydrogen etching has no effect on the morphology of polished (100) GaAs substrates, while thermal oxide desorption roughens the surface. Carbon contamination of the surface causes roughening during subsequent firm growth. Secondary ion mass spectrometry and photoemission spectroscopy show that atomic-hydrogen etching reduces the carbon contamination on the substrate but does not remove silicon oxide. Synchrotron radiation photoemission measurements show that some as-received substrates are contaminated with a thin uniform layer of SiO₂.