Optical anisotropy of oxidized InAs( [formula omitted]) surfaces

Abstract

Reflectance anisotropy spectroscopy (RAS) has been applied to study the oxidation of decapped InAs(0 0 1) surfaces at room temperature. (2×4) and (4×2) surfaces were prepared in ultra high vacuum by annealing, and then exposed to increasing amounts of molecular oxygen. During exposure to gas, RAS spectral structures at 2.4 eV in (2×4) and at 1.7 eV in (4×2) are progressively reduced. After about 1×10 4 L, a broad residual anisotropy spectrum is still measured for (2×4), while relic anisotropy is nearly null for (4×2). Residual features are visible at bulk critical points ( E 1, E 1+ Δ 1 and E 0 ′). The different behavior versus gas contamination evidences the origin of RAS spectral structures, allowing interpretation in terms of surface-state or bulk transitions (the latter modified by the surface). By using Kramers–Kronig relations, the anisotropy of the imaginary part of the surface dielectric function ( Δε ″ s) between [ 1 ̄ 1 0] and [1 1 0] directions of the substrate has been obtained from RAS data. We conclude that the main RAS structures (at 2.4 eV in (2×4), at 1.7 eV in (4×2)) are related to the surface reconstruction, although only the latter is a transition involving true surface states. We observe bulk contributions in coincidence with critical points ( E 1, E 1+ Δ 1 and E 0 ′).