Passivation of the GaAs (100) surface by self-assembled monolayers of octadecylthiol (ODT) has been studied using inelastic light scattering as a probe of the near-surface electronic structure. Application of the ODT self-assembled monolayers reduces the width of the depletion region at the surface of GaAs resulting in a reduction of the surface band bending, and the electron scattering time is increased as well. The ODT passivated surfaces are more stable to environmental degradation, over time and under temperature stress, than inorganic sulfide treated surfaces which have been reported. Organic thiol passivation may provide an attractive alternative to inorganic sulfide protocols for reduction of surface recombination velocities in III–V devices.

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High-quality thin Nb and NbN films ͑60-100 Å͒ are grown on ͑100͒ n ϩ-InAs (nϭ10 19 cm Ϫ3) substrates by dc-magnetron sputter deposition. Studies of the electronic properties of interfaces between the superconductor and the semiconductor are done by Raman scattering measurements. The superconducting proximity effect at superconductor-semiconductor interfaces is observed through its impact on inelastic light scattering intensities originating from the near-interface region of InAs. The InAs longitudinal optical phonon LO mode (237 cm Ϫ1) and the plasmon-phonon coupled modes L Ϫ (221 cm Ϫ1) and L ϩ ͑1100 to 1350 cm Ϫ1), for n ϩ ϭ1ϫ10 19 Ϫ2ϫ10 19 cm Ϫ3 are measured. The intensity ratio of the LO mode ͑associated with the near-surface charge accumulation region, in InAs͒ to that of the L Ϫ mode ͑associated with bulk InAs͒, is observed to increase by up to 40% below the superconducting transition temperature. This temperature-dependent change in light scattering properties is only observed with high quality superconducting films and when the superconductor and the semiconductor are in good electrical contact. A few possible mechanisms of the observed effect are proposed.

Raman scattering by coupled longitudinal optic phonons and two-dimensional electron gas electrons in In0.53Ga0.47As-In0.52Al0.48As δ-doped heterostructures provides a powerful probe of electronic properties in these In-based structures. The two highest frequency modes, of the three coupled electron-phonon modes expected in this system, were observed, with the highest frequency mode being identified in InGaAs-based systems. The large dispersion of this mode makes it a particularly sensitive probe for changes in such properties as carrier concentration and subband energy. For structures with higher carrier concentrations coupling of the longitudinal optic phonon to multiple electron intersubband transitions is resolved. These measurements are particularly useful for heavily doped structures for which room-temperature Hall measurements cannot distinguish channel electrons from those in parallel conduction paths.