For the first time, high-resolution electron-energy-loss spectroscopy (HREELS) measurements of the coupled plasmon and phonon modes on n-type InAs(110) cleaved surfaces were carried out. Core-level shifts observed in ultraviolet photoemission spectroscopy indicate that an accumulation layer is formed near the surface after the surface is exposed to hydrogen. The HREELS spectra show the evolution of the plasmon due to the accumulation-layer formation and its coupling to the phonon. Spectra of different primary energy were also taken to study the dispersion behavior of the plasmon. A model calculation based on a self-consistent free-carrier profile together with the Debye-Hückel description of the local dielectric response was performed to aid the interpretation of the spectra. Reasonable fits to the data were obtained for surface charge deficits in the range of ${10}^{11}$ to ${10}^{12}$ electrons/${\mathrm{cm}}^2$. Evidence for a ‘‘dead layer’’ very near the surface was found for each accumulation layer studied. This work supplements earlier studies of coupled plasmon-phonon modes in III-V semiconductors with depletion layers.

• Received 15 November 1988

DOI:https://doi.org/10.1103/PhysRevB.39.12682