[en] Amorphous and polycrystalline compounds of (Ga,As) and (Al,As) grown at very low temperatures by molecular-beam epitaxy are characterized. The ultimate microstructure and the amount of excess arsenic incorporated in the (Ga,As) or (Al,As) layers are found to depend on the arsenic overpressure during the low-temperature growth. With lower arsenic overpressure, a polycrystalline structure prevails and less excess arsenic is observed inside the layer. In contrast, a high incorporation of excess arsenic achieved by high-arsenic overpressures leads to the formation of amorphous films. Upon wet oxidation, the lateral oxidation rate of (Al,As) is found to depend on the crystallinity of the (Al,As) layer and the amount of excess arsenic. During the same process, recrystallization proceeds in the (Ga,As) layer

[en] The interface when switching from AlAs to GaAs during solid source molecular-beam epitaxial growth is investigated. The growth conditions for the AlAs layers were kept constant except for the As overpressure. Using a valved As cracker cell, we varied the V/III flux ratio from ∼5.0 to ∼25.0. Cross-sectional transmission electron microscopy, photoluminescence spectroscopy, and reflectivity measurements from distributed Bragg reflectors indicate that the material quality tends to improve with increasing dimeric As overpressure. Using secondary ion mass spectroscopy, it is shown that the rough interfaces are due to oxygen accumulation at the AlAs growth front. It is believed that arsenic forms an oxide with the oxygen on the AlAs surface, which is subsequently desorbed away at typical growth temperatures. For samples grown at higher overpressures, there is more arsenic present to remove the oxygen thereby resulting in a smoother interface (c) 2000 American Vacuum Society