Improvement of AlAs-GaAs interface roughness grown with high As overpressures

The interface when switching from AlAs to GaAs during solid source molecula r-beam epitaxial growth is investigated. The growth conditions for the AlAs layers were kept constant except for the As overpressure. Using a valved A s cracker cell, we varied the V/III flux ratio from similar to 5.0 to simil ar to 25.0. Cross-sectional transmission electron microscopy, photoluminesc ence spectroscopy, and reflectivity measurements from distributed Bragg ref lectors indicate that the material quality tends to improve with increasing dimeric As overpressure. Using secondary ion mass spectroscopy, it is show n that the rough interfaces are due to oxygen accumulation at the AlAs grow th front. It is believed that arsenic forms an oxide with the oxygen on the AlAs surface, which is subsequently desorbed away at typical growth temper atures. For samples grown at higher overpressures, there is more arsenic pr esent to remove the oxygen thereby resulting in a smoother interface (C) 20 00 American Vacuum, Society.