[en] The strain relaxation in In_0.25Ga_0.75As and In_0.4Ga_0.6As grown on GaAs substrates at low temperature has been studied before and after laterally oxidizing an underlying Al_0.98Ga_0.02As layer. The relaxation as a function of layer thickness has been measured by cross-sectional transmission electron microscopy and x-ray analysis. It is found that oxidation of the Al_0.98Ga_0.02As layer improves the relaxation of the strained In_xGa_1-xAs layer. Moreover, the interfacial misfit dislocations have been removed, and the threading dislocation density has decreased approximately by one order of magnitude after oxidation

[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] Thermal wet oxidations of GaP and Al_0.4Ga_0.6P at 650 degree sign C for various times have been performed. Comparisons are made on oxidation rates and post oxidation morphology. Transmission electron microscopy shows that when oxidizing GaP, polycrystalline monoclinic GaPO₄·2H₂O forms without noticeable loss of phosphorus. Oxidation for 6 h or more leads to poor morphology resulting in cracks and detachment. A thickness expansion of about 2.5-3 times is noticed as a result of oxidation. In contrast, oxidized Al_0.4Ga_0.6P exhibits much better morphology without cracks or detachment from the substrate. The oxide has an almost amorphous-like microstructure. The oxidation process shows typical diffusion-limited reaction at long anneals. Preliminary work on the oxidation of AlP indicates that the reaction leads to formation of Al₂O₃ and possible volatile P₂O₅ diffusing out of the specimen. Thus, from the structural viewpoint, AlGaP forms a better oxide suitable for device needs. (c) 2000 American Institute of Physics

[en] A comparison of the water vapor oxidation characteristics of AlAs, Al_0.98Ga_0.02As, and an Al_xGa_1-xAs digital alloy was performed. The Al_xGa_1-xAs digital alloy consists of periods of 49 monolayers of AlAs and 1 monolayer of GaAs and has an equivalent composition of x=0.98. Oxidation rates and the structural integrity of the three layers were compared. When oxidized in water vapor, the Al_xGa_1-xAs digital alloy and the AlAs have similar oxidation rates, both of which are twice as fast as the Al_0.98Ga_0.02As layer. Post-oxidation annealing of these samples at 450 degree sign C showed severe delamination at the oxide/GaAs interface in the AlAs sample while the Al_xGa_1-xAs digital alloy sample was not damaged. (c) 2000 American Institute of Physics