Porosity-induced modification of the phonon spectrum of n-GaAs

Porous GaAs layers have been produced by anodic etching of (100)-oriented crystalline substrates in a solution. Scanning electron microscope images showed the formation of submicron pores, the average dimension of the remaining GaAs walls being of about 100 nm. Raman scattering by LO-phonon - plasmon coupled modes, inherent in as-grown crystals, was not observed in the porous layers. Proposed explanations are either the depletion of the GaAs skeleton due to the surface space-charge effect or the decoupling of the LO-phonon and the plasmon modes at the relative large wavevectors transferred in nanostructures. A new Raman scattering peak at , located between the bulk TO and LO frequencies, has been observed in porous layers and attributed to a surface-related phonon.