Microstructure and interfacial properties of laterally oxidized Al_xGa_1-xAs

The oxidation of high Al content Al_xGa_1-xAs has received much attention due to its use in oxide-aperture, vertical-cavity surface emitting lasers (VCSELs) and for passivating AlAs against environmental degradation. We have recently identified the spinel, gamma phase of Al₂O₃ in layers laterally oxidized in steam at 450 °C for x = 0.98 & 0.92 and have seen evidence for an amorphous precursor to the gamma phase. At the interface with the unoxidized Al_xGa_1-xAs, an approximately 17 nm amorphous phase remains which could account for the excellent electrical properties of oxide-confined VCSELs and help reduce stress concentrations at the oxide terminus.