Fully-oxidized AlGaAs heterostructures as broadband passive waveguides for photonic circuit integration

In this paper, we demonstrate propagation losses of less than α=1.0 cm^-1 at both λ₀=1.55 and 0.63 μm for an oxidized Al_0.3Ga_0.7As/Al_0.85 Ga_0.15As waveguide. These loss reductions, and the realization of transparency well above the GaAs band edge, are achieved through both an improved structure (thicker cladding layer, larger Al composition contrast) and a modification to the standard oxidation process (via the controlled addition of O₂). The addition of trace amounts of oxygen reduces the oxide surface roughness, increases the index of oxidized Al_xGa_1-xAs (x<0.5), and increases oxidation rates (0.3<x<0.85). These process enhancements lead to improved mode confinement and reduced absorption and scattering losses