Microstructure and interface properties of laterally oxidized Al{sub x}Ga{sub 1{minus}x}As

The selective and passivating nature of the oxidation of high Al content AlGaAs has been used to create high-performance vertical-cavity surface emitting lasers (VCSELs). This is accomplished by using the fact the Ga content of a AlGaAs film will drastically affect its oxidation rate, allowing the strategic placement of high Al content layers in the structure; these are then oxidized to form current-confining and optical-mode-defining apertures. Here, the microstructure and interface properties of Al{sub x}Ga{sub 1{minus}x}As materials that have been laterally oxidized in wet N{sub 2} for several compositions (x = 0.80, 0.82...1.00) and temperatures (360 C to 450 C) have been studied. The microstructure is found to be relatively insensitive to composition and oxidation temperature. The oxidation forms an amorphous solid solution (Al{sub x}Ga{sub 1{minus}x}){sub 2}O{sub 3} that transforms to polycrystalline, {gamma}-(Al{sub x}Ga{sub 1{minus}x}){sub 2}O{sub 3} is formed via post oxidation annealing of the oxide. The level of hydrogen present in the oxidized layers is 1.1 {times} 10{sup 21} cm{sup {minus}3}, which is too low for the amorphous phase observed to be a hydroxide rather than an oxide. The amount of As in the layer is reduced to <2 atm%, and no As precipitates are observed. The (Al{sub x}Ga{sub 1{minus}x}){sub 2}O{sub 3}/GaAs interface is abrupt, but prolonged oxidation will cause the GaAs to oxidize at the internal interfaces. The reaction front between the oxidized and the unoxidized Al{sub x}Ga{sub 1{minus}x}As has a 10 to 20nm-wide amorphous zone that shows a different contrast than the remainder of the amorphous oxide and is stable under electron irradiation