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Pattern formation in lateral oxidation of aluminum-rich AlxGa1-xAs Nicoll, Christine Anne


A high-aluminum-content AlxGa1-xAs (x > 0.9) layer in an epitaxial III-V semiconductor heterostructure can be preferentially oxidised from an exposed edge at 375-450C in a wet N2 ambient. In this way, buried aluminum oxide layers can be formed which are useful for optical and electronic confinement in III-V devices such as VCSELs and distributed feedback lasers. The rate of oxidation is strongly dependent on aluminum content and is higher in the (001) directions than the (011). We find that an angular dependence of the form a + bsin²2θ accurately describes the anisotropy of the oxidation rate. This anisotropy has the interesting consequence that oxidation proceeding outward from a pinhole evolves into a "rounded-square" shape, while oxidation inward from a circular perimeter produces a square shape. Because of the strong dependence of the oxidation rate on the aluminum content, possibilities exist for lithographic control of oxidised areas by lateral modulation of the composition of the buried layer. The aluminum content of a thin buried aluminum-rich AlxGa1-xAs layer can be reduced by intermixing with neighbouring GaAs layers, using selective-area ion implantation and rapid thermal annealing. This makes it possible to create relatively complex oxide patterns in buried AlxGa1-xAs layers.

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