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Symmetrically modulation doped GaAs/AlxGa1-xAs quantum-well structures, containing a monolayer thickness of single AlAs insertion in the well region, are studied by photoluminescence spectroscopy a ...

The optical properties of indium islands on GaAs(001) surfaces have been studied by reflectance anisotropy spectroscopy as a function of metal coverage. A large optical anisotropy is observed, which shows an oscillatory behavior and scales with the island size: mean island sizes determined by scanning electron microscope correspond to the wavelengths where extremes in the optical anisotropy arise. We explain this behavior by surface plasmon resonances of the island structure which induce a huge optical anisotropy related to the anisotropic shape and distribution of the In islands. Model calculations of the reflectance anisotropy spectroscopy signal based on a layer system where the island film is represented by an effective medium consisting of ellipsoidal metal particles in a vacuum matrix reproduce the main oscillation and support our conclusion.

The indium-stabilized $\mathrm{GaAs}(001)\ensuremath{-}c(8\ifmmode\times\else\texttimes\fi{}2)$ surface was investigated by surface x-ray diffraction and x-ray standing waves. We find that the reconstruction closely resembles the $c(8\ifmmode\times\else\texttimes\fi{}2)$ structure described by the recently proposed unified model for clean III-V semiconductor surfaces [Kumpf et al., Phys. Rev. Lett. 86, 3586 (2001)]. Consistent with this unified model, no In dimers are found for the present surface. Instead, for coverages less than 0.25 monolayers, the In adatoms adsorb at the initially unoccupied hollow sites to form In rows along the [110] direction. Between the In rows, surface and subsurface Ga dimers are found to coexist in the trench areas. Above 0.25 monolayers, the additional In adatoms fill the trenches and replace the surface Ga atoms. The final structure of the surface layer is essentially identical to the InAs clean surface, except that the In heights are substantially different due to the lateral strain induced by the lattice mismatch. This structural difference explains why the ladder-type pattern observed previously by scanning tunneling microscopy only appears for the In/GaAs(001) and InAs/GaAs(001) surfaces, but not for the InAs clean surface. The structural model we propose for the In-stabilized $\mathrm{GaAs}(001)\ensuremath{-}c(8\ifmmode\times\else\texttimes\fi{}2)$ surface, which fully agrees with the scanning tunneling microscopy results, should therefore generally apply to strained InAs(001) surfaces.

Surface modifications induced by germanium deposition onto clean GaAs(001) substrates have been monitored by reflectance anisotropy spectroscopy (RAS) and low energy electron diffraction (LEED). The clean GaAs(001) surfaces onto which Ge has been evaporated were c(4X4), (2X4), and (4 × 1) reconstructed. Regardless of the initial surface reconstruction, after deposition of 0.5 monolayers of Ge and further annealing at 850 K, we have always observed a (1 × 2) LEED pattern and the same characteristic RAS spectrum. On the contrary, overlayer structures obtained at intermediate stages between the clean surface and this (1 × 2) phase depend upon the initial surface reconstruction. Modifying the (1 × 2) reconstructed surface by deposition of additional monolayers of Ge or exposure to atmosphere, we have separated the surface, interface, and bulk contributions to the RAS spectra. Finally, monitoring the characteristic linear-electro-optical feature appearing at E 1 and E 1 + Δ 1 bulk critical points, we discuss how its change in amplitude and sign could be connected to a variation of the substrate doping induced by annealing.