Reduction of etched AlGaAs sidewall roughness by oxygen-enhanced wet thermal oxidation

The authors demonstrate that the oxidation smoothing of sidewall roughness of dry-etched Al0.3Ga0.7As ridge structures is enabled through a modified wet thermal oxidation process which involves the addition of dilute amounts of O2 to the water vapor ambient. High magnification cross-section and top-view scanning electron microscope imagings both before and after oxide removal clearly show a substantial reduction of photolithography- and dry-etching-induced sidewall roughness (from σ∼100nm down to σ∼1–2nm), occurring only with the participation of added O2. The smoothing process provides means to realize high-index-contrast GaAs-based optical waveguides with both low bend and scattering losses.