Nonselective Wet Oxidation of AlGaAs Heterostructure Waveguides Through Controlled Addition of Oxygen

We present data showing that the addition of trace amounts of O₂($≪1hbox%$relative to N₂) to N₂+H₂O process gas during the wet thermal oxidation of Al_ xGa₁ -xAs enhances the oxidation rates of lower Al content$( xle 0.8)$alloys (a tenfold increase for$ x=0.3$), while decreasing the oxidation rate selectivity$ R( x=0.8)/ R( x=0.3)$by a factor of seven. An increase in the refractive index from 1.49 to 1.68, and a fourfold decrease in surface roughness, indicates the formation of a denser, higher quality oxide for$ x=0.3$AlGaAs. Oxides are characterized by prism coupling, atomic force microscopy, and scanning electron microscopy. Thermochemical calculations show a probable mechanism in the enhancement of the dry oxidation reactions of AlGaAs for low levels of O₂, while there is still an adequate quantity of H₂produced to reduce As oxides in the wet oxidation process. An AlGaAs quantum well heterostructure p-n laser diode crystal is nonselectively oxidized to create a deep oxide, high-index contrast waveguide with potential applications in semiconductor photonic integrated circuits that require small bend radius, high isolation, low crosstalk optical waveguides.